Osteology of the Clupeiform fish, genus Hyperlophus (II)

Bull. Kitakyushu Mas. Nat. Hist., 4: 77-102. December 31, 1982 Osteology of the Clupeiform fish, genus Hyperlophus (II) Yoshitaka Yabumoto Kitakyushu Museum of Natural History, Nishihonmachi, Yahatahigashiku, Kitakyushu, 805 Japan and Teruya Uyeno National Science Museum, Tokyo, 160 Japan Description Shape ofneurocranium The distance from the anterior end of the prevomer to the posterior end of the epiotic is about 2.4 times of the depth at the foramen for the internal carotid arteries of the parasphenoid in Hyperlophus vittatus, but about 2.0 times in H. translucidens. The maximum width of the cranium is at the pterotic. The width is equal to the depth in H. vittatus, but in H. translucidens the width is slightly shorter than the depth. The cranial cavity occupies about two-fifth of the total neurocranial length. The cranial roofspace are larger in H. translucidens (Fig. 2 and 3). Olfactory Region Ethmoid (eth). The lateral process for the palatine (lpp) and the dorsal process are present on the anterior end of the ethmoid. The ligaments from the maxillaries are attached to the upper end of the dorsal process which is laterally widened. Internally the condyle of the palatine attaches to the tip of the lateral process of the ethmoid (lpp). The cranial condyle of the maxillary (cc) is attached to the area between the lateral process and the dorsal process of the ethmoid. The posterior part of the ethmoid is divided to right and left. The posterior half of the ethmoid is attached to the inner surface of the frontal. The anterior part of the ethmoid is deeper in H. translucidens than in H. vittatus. The suture between the prevomer and the ethmoid is wider in H. translucidens than in H. vittatus (Fig. 2 and 3). Prevomer (prev). The prevomer consists of the thick head with a pair of small lateral processes and a spear-shaped shaft which posteriorly extends beneath the prefrontal. The teeth is absent on the prevomer. The anterior

78 Yoshitaka Yabumoto and Teruya Uyeno margin of the prevomer is round. The head of the prevomer is broader in H. translucidens than in H. vittatus. The suture between the prevomer and the ethmoid is broader in H. translucidens than in H. vittatus. In H. translucidens the posterior part of the prevomer, which is in contact with the parasphenoid, becomes narrower and the constriction is present between the prevomer and the parasphenoid in the ventral view. In H. vittatus the posterior part of the prevomer gradually becomes narrower and the constriction is absent (Fig. 2 and 3). Prefrontal (pref). The prefrontal sutures with the underside of the ante rior end of the frontal. The prefrontal is not in contact with the ethmoid, and a cartilage is present between them. The prefrontal curves antero-laterally as a wing and is ventrally separated from the parasphenoid (para) by a cartilage. The dorsal process (pplm) of the endopterygoid is strongly connected to the prefrontal by a cartilaginous process. This structure forms the anterior wall of the orbit. Each prefrontal comes into contact by a cartilage in H. vittatus. In H. translucidens each prefrontal mutually comes into contact without a cartilage. The prefrontal sutures with the orbitosphenoid in H. translucidens. In H. vittatus the prefrontal is connected to the orbitosphenoid by a cartilage. The canal of the olfactory nerve pierces obliquely through the inside part of the prefrontal. In H. vittatus the anterior opening of the olfactory nerve is a circle, but it is a broken circle in H. vittatus, in examined specimens. Nasal (nas). The nasal is a pair of small bones and situated above the orfactory organ. The nasal is U-shaped in cross section and forms a groove. Two or three foramina are present (Fig. 4B and E). Orbital Region Orbitosphenoid (ors). The orbitosphenoid (ors) lies anterior to the pterosphenoids (pte). The dorso-anterior margin of the orbitosphenoid forms the ventral margin of the large foramen for the olfactory tracts. The posterior margin of the orbitosphenoid forms the optic foramen (of) with the pterosphenoid. A pair of foramina is present on the orbitosphenoid. Antero-ventrally the orbitosphenoid is produced as membranous interorbital septum. In H. translucidens the interorbital septa are divided into anterior and posterior parts. In H. vittatus the anterior and posterior septa are divided or, connected by a low septum. The small bony septum lies before the anterior septum which is contact with the prefrontals and parasphenoid by a cartilage in H. vittatus. In H. translucidens the anterior septum sutures with the prefrontals which are separated from the parasphenoid by a cartilage. Dorsally, the plate-like curved processes, which are attached with the frontals, are raised on the postero-lateral corner ofthe orbito sphenoid (Fig. 2 and 3). Basisphenoid. The basisphenoid is U-shaped bone. The ventral margin

Osteology of the Clupeiform fish, genus Hyperlophus (II) 79 of the optic foramen is formed by the dorsal margin of the basisphenoid. The ventral and lateral parts of the basisphenoid are in contact with the prootics and laterally form a pair of openings and one large opening ventrally. The dorso lateral end of the basisphenoid is in contact with the pterosphenoid in H. translucidens, but in H. vittatus it is overlapped by the pterosphenoid. Pterosphenoid (pte). The paired pterosphenoids form the posterior wall of the orbit with the frontals, autosphenotics, prootics, and basisphenoid. The anterior margin of the pterosphenoid is in contact with the orbitosphenoid. The optic foramen is formed by the pterosphenoids and orbitosphenoid. The pterosphenoid is in contacts with both the frontal and autosphenotic laterally and forms the foramen of the trigeminal nerve (V) with the prootic posteriorly. In H. vittatus one or two small openings are present on the pterosphenoid. In H. translucidens the opening is absent (Fig. 2 and 3). Frontal (fro). The paired frontals occupy about 60 percent of the total cranial length. Each frontal is narrow anteriorly and widens posteriorly. Posteriorly each frontal ends complicated, with a overlap above the pariatal, supraoccipital, and pterotic. The interfrontal suture is straight posteriorly and is anteriorly separated by a cartilage. Anteriorly each frontal is attached with the inner surface of the ethmoid. The supraorbital canal of the lateral line system is in a bony tube and groove. The nasal opening is separated by a transverse bony strap from the interorbital opening. The bony strap is long in H. vittatus. It is short in H. translucidens. Three or four openings are present on the under surface of each frontal in both species. Each supraorbital canal meets with a canal from another side by a anterior short bony tube on the middle of the frontal roof. There is a slender, short branched bony tube, which curves postero-dorsally, behind the anterior bony tube. Two dorsal and one ventral small openings are present between two branched tubes in H. translucidens. These are absent in H. vittatus. The postorbital opening of the supraorbital canal is large, a gourdshaped, and is formed by the autosphenotic, frontal, and pterotic. Both species have a recessus lateralis (in which the infraorbital, supraorbital, and preopercular sensory canals converge). The anterior part of the postorbital opening is connected to the infraorbital canal. The posterior part of the postorbital opening is connected to the supratemporal and preopercular canals. The slender ridge is present on the posterior roof of the frontal (Fig. 2 and 3). Infraorbitals (inf). Six infraorbitals are present. The third infraorbital (inf 3) is the largest. The sixth infraorbital (inf 6) lies on the autosphenotic and connects the infraorbital canal to the postorbital opening of the supraorbital canal. The orbital shelf is absent. The infraorbital sensory canal runs on the infraorbitals and each infraorbitals bears a flange overhanging the canal. The anterior end of the canal on the first infraorbital passes through a short bony tube in H. vittatus. The bony tube is absent on the first infraorbital in H.

80 Yoshitaka Yabumoto and Teruya Uyeno translucidens. The boundary between the first and the second infraorbital is distinct in H. vittatus. It is indistinct in H. translucidens. The anterior groove of the second infraorbital for the sensory canal is narrower in H. translucidens than in H. vittatus. In H. vittatus the boundary between the third and the forth in fraorbital of the left side is indistinct, but this boundary of the right side is dis tinct in the figured specimen. The third infraorbital is larger in H. translucidens than in H. vittatus (Fig. 4B and E). Supraorbitals (supr). The supraorbitals are two in number. The posterior supraorbital (supr 1) is larger than anterior one (supr 2). The first supraorbital (supr 1) is twisted at the central part, with one ridge extending throughout its length. The posterior end of the first supraorbital reaches at the center of upper margin of the orbit. The second supraorbital (supr 2) is thin and curved. The posterior end of the second supraorbital separates slightly from the anterior end of the first supraorbital. The anterior half of the second supra orbital overlies on the upper margin of the first infraorbital. The second supra orbital is broader in H. translucidens than in H. vittatus (Fig. 4B and E). Otic Region Autosphenotic (sph). The anterior face of the autosphenotic forms the posterior wall of the orbit with the prootic and pterosphenoid. The autosphenotic comes in contact with the pterosphenoid and frontal dorsally, and with the prootic ventrally. The lateral frange of the autosphenotic connected to the lateral edge of the frontal extends laterally as a wing. The ventro-inner process of the autosphenotic forms a bridge with the antero-ventral edge of the prootic. The lateral face of the autosphenotic forms the anterior postorbital opening of the supraorbital canal. The facet for the hyomandibular is present under the postorbital opening of the supraorbital canal and lies on the pterotic and auto sphenotic. The anterior two-third of the facet for hyomandibular lies along the border of the autosphenotic on the ventral face (Fig. 2, 3, and 4). Pterotic (pto). The pterotics are complicated bones and form the postero-lateral region of the neurocranium. The pterotic is anteriorly in contact with the frontal, antero-ventrally with the autosphenotic, and posteriorly with exoccipital and epiotic. The pterotic forms the posterior postorbital opening of the supraorbital canal. The shallow and short groove following the supratemporal is present behind the postorbital opening on the pterotic. In H. vittatus the dorsal end of the pterotic is separated from the parietal by a large cartilage, which is surrounded by the frontal, parietal, pterotic, and epiotic. In the large specimen of H. vittatus, the pterotic is partly overlapped by the anteroventral part of the parietal which forms the swelling for the anterior vertical semicircular canal. In H. translucidens the dorsal end of the pterotic is overlapped by the parietal and the small catilage is surrounded by the frontal, parietal and

Osteology of the Clupeiform fish, genus Hyperlophus (II) 81 pterotic. There are the swelling for the horizontal semicircular canal on the center of the bone and the swelling for the anterior vertical semicircular canal on the antero-dorsal part of the pterotic in both species. The swelling for the pos terior vertical semicircular canal is present on the postero-dorsal part of the pterotic in H. vittatus. It is formed by the exoccipital and epiotic in H. translucidens. The round swelling on the dorso-medial part of the pterotic is larger in H. translucidens than in H. vittatus. The posterior one-third of the facet for the hyomandibular lies on the ventral face of the pterotic (Fig. 2, 3, and 4). Epiotic (epo). The epiotics form the lateral part ofthe posterior cranial surface with the exoccipitals. The swelling for the posterior vertical semicircular canal lies on the main body of the epiotic. In the posterior view, the epiotics are separated each other by the exoccipitals and supraoccipital. The epiotic is dorsally in contact with the supraoccipital by a cartilage and sutures with the palatine dorso-anteriorly. The inner margin of the epiotic is overlied by the exoccipital in H. translucidens. In H. vittatus the epiotic is separated from the exoccipital by a cartilage. In the lateral view, the anterior margin of the epiotic overlies the pterotic in H. translucidens. The anterior margin of the epiotic is ventrally in contact with the pterotic. The swelling for the ventral part of the posterior vertical semicircular canal is formed by the pterotic, exoccipital, and epiotic in H. vittatus. This swelling is formed only by the epiotic in H. translucidens (Fig. 2 and 3). Intercalar (inca). The intercalar forms a cap over the triradiate union of the exoccipital, epiotic and pterotic. The ventral process of the posttemporal (ppi) is attached to the intercalar. The intercalar is larger in H. vittatus than in H. translucidens (Fig. 2, 3, and 4). Exoccipital (exo). The exoccipital exhibits both a lateral and posterior face. The posterior face is in contact with the epiotic and supraoccipital above, and the basioccipital below, and surrounds the foramen magnum with its fellow of the opposite side and the basioccipital. The each exoccipital is slightly sepa rated by a cartilage above the foramen magnum. The exoccipital slightly overlaps the epiotic and the dorsal margin of the exoccipital runs along the margin of the supraoccipital in H. translucidens. The exoccipital is clearly separated from the epiotic by a cartilage and the dorsal margin is round in H. vittatus. The lateral face of the exoccipital is in contact with the pterotic anteriorly and the prootic antero-ventrally. The large foramen for glossopharyngeal nerve is formed by the exoccipital, basioccipital, and prootic. The foramen for vagus nerve (V) pierces the postero-ventral surface of the exoccipital. The swelling for the ventral part of the posterior vertical semicircular canal is formed by the antero lateral part ofthe exoccipital and the posterior part ofthe pterotic in H. vittatus. The swelling is formed only by the antero-lateral part of the exoccipital in H. vittatus. In H. vittatus two or three openings are present on the postero-lateral

82 Yoshitaka Yabumoto and Teruya Uyeno surface of the exoccipital. These are absent in H. translucidens (Fig. 2 and 3). Supraoccipital (supo). The postero-medial end of the cranial roof is formed by the supraoccipital. The supraoccipital is a complicated bone. In the dorsal view, the part near the posterior end of the supraoccipital is narrow and the anterior part is flat, and is overlapped by each frontal. The shape of the flat part of the supraoccipital is variable, wide and round or narrow and long. The supraoccipital crest is small and low on the postero-medial end of the supraoccipital roof. The pair of the cartilaginous area are surrounded by the supraoccipital, frontals, and parietals on the cranial roof. The cartilaginous area on the roof is seen in the lateral view of the cranium, because the anterior part of the supraoccipital forms a bridge in H. translucidens, but the cartilaginous area is not seen in H. vittatus, because the anterior part of the supraoccipital is straight. The weak vertical ridge is present on the middle of the posterior surface of the supraoccipital following from the supraoccipital crest. The ventral margin of the supraoccipital is round and separated from the exoccipitals by a cartilage in H. vittatus, but in H. translucidens it is not round and runs parallel to the dorsal margin of the exoccipitals. The anterior and posterior vertical semicircular canals meet mutually inside of the postero-lateral parts of the supraoccipital which are overlapped by the parietals and are in contact with the epiotics (Fig. 2 and 3). Parietal (pari). Anteriorly the parietals are overlapped by the frontals in a greater extent. Parietals are separated for a great distance by the supra occipital. Posteriorly the parietals overlap the supraoccipital and epiotics. Two parallel franges are present and form a vertical groove on the epiotic. The anterior frange is larger than the posterior one. The upper limb of the posttemposral is stoutly attached behind the posterior frange of the epiotic. In H. vittatus the ventral end of the parietal is separated from the pterotic by the large cartilage, which is surrounded by the frontal, pterotic, epiotic and parietal. In the large specimen of H. vittatus, the antero-ventral part of the parietal, which forms the swellingfor the anterior vertical semicircular canal, overlaps the pterotic. In H. translucidens the ventral part of the parietal overlaps the pterotic and the small cartilage is surrounded by the frontal, pterotic and parietal. The swelling for the anterior vertical semicircular canal is present of the anterior part of the parietal (Fig. 2, 3, and 4). Basicranial Region Basioccipital (bas). The basioccipital lies between the paired exoccipitals. The anterior margin of the basioccipital is in contact with the prootics by a cartilage. The antero-dorsal margin of the basioccipital forms the foramen for the glossopharyngeal nerve (IX) with the prootic and exoccipital. The paired exoccipitals overlap the dorso-posterior portion of the basioccipital to greater extent. In the posterior view, the basioccipital forms the foramen magnum

Osteology of the Clupeiform fish, genus Hyperlophus (II) 83 with the paired exoccipitals. The ventro-lateral wings of the basioccipital contacting with the parasphenoid form the deep groove for the myodom with the posterior wings of the parasphenoid. The posterior face of the basioccipital articulates with the first centrum (Fig. 2, 3, and 4). Parasphenoid (para). The parasphenoid is long and curved. An teriorly the parasphenoid is in contact with the prevomer and posteriorly extends beyond the posterior surface of the cranium. A median longitudinal ridge is present on the dorsal surface of the bone beneath the orbit. The posterior part of the parasphenoid forms the foramen leading to the myodom as a deep ascending wings, which are divided right and left by the deep notch in the ventral view. The dorsal margin of this wing is in contact with the prootic and basioccipital. A pair of foramina for the internal carotid arteries occur within the parasphenoid before the deep notch. The upper pharyngeals articulate with the parasphenoid near the foramen for the internal carotid arteries. The articulated part of the parasphenoid for the upper pharyngelas forms a notable ridge in H. translucidens. In H. vittatus the articulated part forms a low ridge (Fig. 2, 3, and 4). Oromandibular Region Palatine (pal). The palatine is a splint-shaped bone. The teeth are absent. The anterior end of the palatine is a protuberance which is attached to the lateral process of the ethmoid (lpp) adaxially. The premaxillary-palatine and maxillary-palatine ligaments originate from the antero-dorsal end of the palatine. Externally the anterior protuberance is articulated with the maxillary by a soft tissue. The flange lies on the dorsal edge of the palatine and is reduced posteriorly. Ventrally the posterior half of the palatine is in contact with the ectopterygoid (Fig. 6 and 7). Ectopterygoid (ecp). The ectopterygoid is formed of a crooked main body and thin bony process (pplm) extending dorsally from the angle of the bone for the prefrontal. The bony process (pplm) is firmly connected with the pre frontal by a cylindrical cartilage. The dorso-anterior limb of the ectopterygoid is in contact with the palatine anteriorly and with the endopterygoid posteriorly. Posteriorly the ventral limb of the ectopterygoid forms a groove which fits the quadrate. The ventral limb is shorter than the dorso-anterior limb (Fig. 6 and 7). Endopterygoid (enp). The endopterygoid is concave to line the eye ball except for a ventral area which lie flush with the surface of the ectopterygoid and quadrate. The teeth are absent on the bone. The anterior part of the endopterygoid lies on the ectopterygoid. The ventral area of the endopterygoid is narrow in H. vittatus. It is broad and concave ventrally at the middle part of the bone in H. translucidens. (Fig. 6 and 7). Metapterygoid (met). The metapterygoid is a cancellous bone fitting into the curve formed by the quadrate, symplectic, and hyomandibular. The

84 Yoshitaka Yabumoto and Teruya Uyeno posterior margin of the metapterygoid is overlapped by the dorsal margin of the endopterygoid. Two notches are present on the postero-dorsal margin of the metapterygoid. The upper notch overlaps the ventral edge of the anteroventral wing of the hyomandibular. The postero-ventral margin of the meta pterygoid fits into the groove near the ventral end of the hyomandibular shaft. A fenestra is formed by the posterior margin of the metapterygoid and the wing and shaft of the hyomandibular. The metapterygoid is separated from both the quadrate and symplectic by a narrow strip of cartilage. Two notches of the postero-dorsal margin are deep in H. vittatus. These are shallow in H. tanslucidens. The postero-ventral margin is somewhat straight in H. vittatus. In H. translucidens it is concave at the middle part (Fig. 6 and 7). Quadrate (qua). The quadrate is a triangular bone. The ventral apex forms a condyle articulating with the depression in the angular. Externally the short ridge extends posteriorly from the condyle of the quadrate. The anterior margin is in contact with the groove of the ectopterygoid. The ventral margin is in contact with the upper edge of the horizontal limb of the preopercle. On the inner surface along the ventral edge of the quadrate lies the symplectic, connecting the quadrate with the hyomandibular. The postero-dorsal apex of the quadrate is acuminate. The dorsal margin of the quadrate is convex anteriorly in H. translucidens. The dorsal margin is slightly convex, somewhat straight, in H. vittatus. The antero-dorsal apex of the quadrate is in acute angle in H. vittatus. It is nearly at right angle in H. translucidens (Fig. 6 and 7). Premaxillary (prem). The premaxillary is a small bone with a vertical ridge and lies on the dorsal head of the maxillary. The small ascending process (asp) is present at the dorsal end of the premaxillary. The articular condyle for the maxillary (arp) is present on the underside of the bone. The premaxilllarypalatine ligament originates from the external surface of the premaxillary near the dorsal end. Both premaxillaries overlap each other at the median. The ar ticulated part of the underlying bone is produced on the outline. The articulated part of the overlying premaxillary is round at this part. It is individually variable as to which side is the upper premaxillary. The vertical ridge is distinct and the anterior part is thick in H. vittatus. In H. translucidens this ridge is weak (Fig. 6, 7 and 8). Maxillary (max). The anterior part of the maxillary is a stout shaft with a narrow flange and curves both dorsally and medially. The posterior part of the maxillary is thin as a wing with the minute teeth. The dorsal end of the maxillary is triangular and articulates with the articular process of the pre maxillary (arp) by the anterior condyle (pc), and with the ethmoid by the posterior condyle (cc). There are posteriorly two condyles near the dorsal end of the maxillary. The upper process (pmp) articulates with the palatine by a soft tissue. The base of the lower process (pirns) is connected to the second supraorbital by

o r.a supm Figure 8. The snout region in the dorsal viewof the H. vittatus. right: after removal of premaxillaries.

Figure 9. The scales of H. vittatus.

Osteology of the Clupeiform fish, genus Hyperlophus (II) 87 the ligament. The maxillary-maxillary ligament attaches to the center of the each triangular head of maxillary. The maxillary-ethmoid ligament connects the maxillary to the dorsal process of the ethmoid over the maxillary-maxillary ligament. The maxillary-palatine ligament originatesfrom the external surface of the maxillary near the cranial condyle (cc). The anterior part of the maxillary is broader in H. translucidens than in H. vittatus. The teeth of the maxillary are smaller in H. translucidens than in H. vittatus. In H. vittatus the posterior wing of the maxillary bears five or six rows of the teeth on the external surface, but in H. translucidens the teeth are very minute and the teeth rows are indistinct (Fig. 6, 7 and 8). Supramaxillary (suprm). There is a pair of supramaxillaries. The anterior part of the supramaxillary is narrow and lies along the dorso-median margin of the maxillary. The posterior part of the supramaxillary is broad and overlaps the postero-dorsal part of the maxillary. The supramaxillary is mobile. The posterior part of the supramaxillary is deeper in H. vittatus than in H. translucidens (Fig. 6 and 7). Dentary (den). The dentary is a large and deep bone. The part near the anterior margin of the dentary is thick. Minute teeth are present on the antero-ventral margin of the dentary and slightly larger than the maxillary teeth. The groove for the sensory canal is present along the ventral edge of the dentary. The dentary bears a flange overhanging this groove. The anterior and posterior ends of the flange form a bony tube. Externally a large concavity is present on the antero-ventral part of the dentary. The posterior margin of the dentary is V-shaped. Posteriorly the inner surface of the dentary is attached by the angular. Three or four teeth are present on the dentary in H. vittatus. Two to five teeth in H. translucidens. The teeth are larger in H. vittatus than in H. translucidens. The embayment is present on the anterior margin near the anterodorsal corner of the dentary (Fig. 6 and 7). Angular (ang). The angular is a triangular bone. The anterior margin of the angular concave in a V-shape. Anteriorly the ventral limb of the angular is attached to the inner surface of the dentary. The dorso-anterior limb of the angular is attached to the inner surface ofthe dentary and forms the dorsal margin of the lower jaw with the dentary. Meckel's cartilage lies on a inner narrow ridge along the lower margin of the ventral limb of the angular. The groove for the mandibular sensory canal is present on the postero-ventral part ofthe angular. This groove bearing a flange slightly extends backward the beyond depression for the quadrate (Fig. 6 and 7). The coronomeckelian is slightly separated forward from the endosteal process of the angular. Retroarticular (ret). The retroarticular is a small bone and attaches to the inner surface of the angular beneath the depression for the quadrate. In

88 Yoshitaka Yabumoto and Teruya Uyeno the external view of the lower jaw, the ventral thick part of the retroarticular is seen. The dorsal part of the retroarticular is thick and V-shaped which attaches to the small facet of the angular. The retroarticular is connected to the epihyal by the ligament (Fig. 6 and 7). Hyoid Region Hyomandibular (hyo). The hyomandibular is a large element with a broad head which is inclined antero-ventrally. The hyomandibular ventrally becomes a narrow shaft, and antero-ventrally expanded as a broad wing. The head of the hyomandibular articulates with the facet on both the autosphenotic and pterotic. In H. translucidens the head of the hyomandibular is divided into the expanded anterior (ace) and posterior parts (pec), which are capped by the cartilage, and cartilaginous condyles are separated. In H. translucidens a notch is present on the center of the dorsal margin of the hyomandibular head in the figured specimen. In H. vittatus the expanded anterior (ace) and posterior ends (pec) of the head are connected mutually without a notch and the cartilaginous condyles on the both ends are connected by a low cartilaginous band. The ante rior cartilaginous condyle articulates with the sphenotic and the posterior one articulates with both the sphenotic and pterotic. The articulated part of the posterior cartilaginous condyle with the sphenotic is shorter in H. translucidens than in H. vittatus. Dorsally the posterior margin of the hyomandibular projects as a prominent opercular process (pph) which is articulated with a cup-shaped de pression of the opercle. The hyomandibular trunk of the facial nerve pierces the hyomandibular beneath the anterior condyle for the cranium (ace) and externally runs on the groove of the ventral shaft. The foramen for the hyomandibular trunk of the facial nerve (fhm) on the inner surface is slightly larger in H. vittatus than in H. translucidens. The posterior ridge along the groove for the hyomandibular trunk of the facial nerve fits to the dorso-anterior margin of the preopercle. The vertical ridge lies on the hyomandibular from the part beneath the anterior condyle for the cranium (ace) to the ventral shaft. The antero-ventral wing of the hyomandibular is curved and overlapped by the meta pterygoid at the antero-ventral margin. This wing is larger in H. translucidens than in H. vittatus. This wing in H. vittatus is a half of the one in H. translucidens (Fig. 6 and 7). Symplectic (sym). The symplectic is antero-ventrally narrow and widens postero-dorsally. The anterior part of the symplectic fits into the groove on the inner surface of the quadrate. The posterior part of the bone is in contact with the inner surface of the horizontal limb of the preopercle. The posterior end of the simplectic meets both the ventral end of the hyomandibular and the dorsal end of the interhyal. Each bone is separated by a narrow strip of carti lage. The posterior end of the simplectic is convex or straight (Fig. 6 and 7).

Osteology of the Clupeiform fish, genus Hyperlophus (II) 89 Interhyal (inh). The interhyal is a small and cylindrical bone. The ventral end of the interhyal is thicker than the dorsal end and is capped by a cartilage which articulates with the posterior tip of the epihyal. The ligament between the interhyal and the epihyal originates from the posterior part near the ventral end of the interhyal. The dorsal end of the interhyal is capped by the small cup-shaped cartilage articulating with the cartilage between the symplectic and the hyomandibular (Fig. 6 and 7). Epihyal (eph). The epihyal is a triangular bone. Its broad anterior end articulates with the ceratohyal by a narrow strip of cartilage. The small process extending antero-dorsally near the posterior end of the epihyal is capped by a cartilage and is articulated to the interhyal. The ligament between the epihyal and the interhyal originates from the posterior end of the epihyal. The groove (gha) for the hyoidean artery continues to the ceratohyal. The small process (per) for the ligament between the epihyal and the retroarticular is present on the epihyal near the posterior end of the groove for the hyoidean artery. Fourth branchiostegal ray (bra 4) is borne on the epihyal (Fig. 6 and 7). Ceratohyal (chy). Posteriorly the ceratohyal is separated from the epihyal by a narrow strip of cartilage. Anteriorly the ceratohyal is separated from the upper and lower hypohyals by a cartilage. The groove for hyoidean artery (gha) horizontally traverses on the dorsal part of the ceratohyal. The groove for hyoidean artery (gha) forms the short bony cannal at the anterior end and forms a groove on the inner surface of the middle part and on the external surface of the posterior end. Posteriorly the groove for the hyoidean artery continues to the epihyal. The anterior opening of the groove for the hyoidean artery lies on the dorsal margin of the ceratohyal near the anterior end. Three branchi ostegal rays attach to the ventral margin of the ceratohyal. The ventral edge of the ceratohyal bears the small notches on which the first and second branchiostegal rays are inserted. The third branchiostegal ray is attached to the external surface of the postero-ventral corner of the ceratohyal (Fig. 6 and 7). Hypohyals (hyph). The hypohyals consist of the upper and lower bones connecting to the ceratohyal with the cartilage. The hypohyals ossify on the surface without inner part. The upper hypohyal (hyph up) is smaller than the lower bone (hyph lo) and is firmly connected between the basihyal and the first basibranchial by the ligament. The lower hypohyal is double a size of the upper bone and is connected with the upper bone by the cartilage. The cartilaginous condyle of the antero-ventral corner of the ceratohyal is articulated with the depression of the lower hypohyal (Fig. 6 and 7). Basihyal (bah). The basihyal is a slender bone and the anterior tip is acuminate. The teeth are minute. The basihyal is antero-ventraly curved. Posteriorly the basihyal articulates with the paired hypohyals and first basi branchial. Three or four teeth are present on the basihyal in H. translucidens,

90 Yoshitaka Yabumoto and Teruya Uyeno about twenty or more in H. vittatus (Fig. 5A). Branchiostegals (bra). Four branchiostegal rays are present. The anterior two branchiostegal rays are inserted on the notches of the ventral margin of the ceratohyal and the third branchiostegal ray is attached to the external surface of the postero-ventral corner of the ceratohyal. Fourth branchiostegal ray is attached to the external surface of the epihyal. The anterior margin of all branchiostegal rays are anteriorly convex in H. vittatus. The fourth branchios tegal ray is not anteriorly convex in H. translucidens. The anterior convex part of the first branchiostegal ray is largest in H. vittatus. The anterior convex part of the second branchiostegal ray is largest in H. translucidens. The posterior end of the third branchiostegal ray truncate and the fourth branchiostegal ray is postero-dorsally curved and posterior end is acuminate. The posterior end of the first branchiostegal ray is acuminate and the posterior end of the second branchiostegal ray is round in H. vittatus. The posterior end of the first branchi ostegal ray is round and the posterior end of the second branchiostegal ray is acuminate in H. translucidens (Fig. 6 and 7). Urohyal. The anterior end of the urohyal is forked into two processes (pul). Each process (pul) is attached to the lower hypohyals by the long liga ments. The distance between both processes of the urohyal is broader in H. translucidens than in H. vittatus. Posteriorly the urohyal broadens to form lateral flanges on its ventral surface. The thin crest extends dorsally. The dorsal margin of this crest is slightly concave. In the ventral view, the low ridge extends posteriorly to continue to the posterior part of the crest. Preopercle (preo). The preopercle is crescent-shaped and traversed throughout its length by the flange and canal overhanging the preopercular sensory canal. The bony canal for the preopercular sensory canal lies on the dorsal part of the preopercle. Dorsally the preopercularsensory canal meets with the supraorbital canal. The bony canal is longer in H. translucidens than in H. vittatus and about double of the length in H. vittatus. The bony canal lies on the dorsal half of the dorsal vertical limb of the preopercle in H. translucidens. The foramina for the external mandibular branch of the facial nerve are present on the inner surface of the preopercle. Three foramina are present on dorsal vertical limb and three are present on the horizontal limb of the preopercle in H. vittatus. Two foramina are present on dorsal limb and three foramina are present on the horizontal limb in H. translucidens. The anterior margin of the preopercle is thin and attached to the third and forth infraorbitals. The anterior edge of the dorsal vertical limb is in contact with the hyomandibular. The upper edge of the horizontal limb of the preopercle is in contact with the quadrate and symplectic. The part between the anterior margin and the angle of the flange for the sensory canal (fcps) is broader in H. translucidens than in H. vittatus (Fig. 6).

Osteology of the Clupeiform fish, genus Hyperlophus (II) 91 Opercle (ope). The anterior border is overlapped by the preopercle and ventrally it narrowly overlaps the subopercle. Dorsally the opercle extends beyond the level of the dorsal ends of the preopercle and hyomandibular. The groove, V-shaped in cross section, runs parallel with the anterior margin of the opercle. The anterior part before the groove is thick. The triangular process of the dorso-anterior corner forms a large depression with the inner bony plate on the opercle. The facet (fo) for the opercular process of the hyomandibular is adaxially supported by the thick part of the anterior margin and the short thick part extending postero-ventrally. The short thick part behind the facet for the hyomandibular is posteriorly convex and round in H. vittatus. It is a straight ridge in H. translucidens. The opercle is wider in H. vittatus than in H. translucidens. The anterior margin of the dorsal part of the preopercle is concave in H. vittatus. It is convex in H. translucidens (Fig. 6 and 7). Subopercle (subop). Dorsally the subopercle is narrowly overlapped by the opercle. Anteriorly the subopercle is overlapped by the interopercle. The thick process of the subopercle extends upward in front of the opercle. The posterior margin of this process fits to the ventral end of the anterior margin of the opercle. The antero-ventral corner of the subopercle is round in H. vittatus. It is square in H. translucidens (Fig. 6 and 7). Interopercle (ino). The interopercle is narrow and thin. The small notch is present on the anterior end of the interopercle. The dorsal margin is undulant. The posterior margin is round and overlaps narrowly the subopercle (Fig. 6 and 7). Branchial Region The hypo-, cerato-, and epibranchial have a groove on those ventral surface which partly surrounds the branchial arteries and bears the gill filaments. Basibranchials (bab). The three basibranchial bones lie in a median series on the floor of the pharynx. The second basibranchial bone is largest. The basibranchial plate bearing teeth lies on the basibranchials (from the first basibranchial to the anterior end of the third basibranchial). The teeth are minute as the basihyal teeth. The tooth rows are present on the posterior and anterior parts of the basibranchial plate, but not on the middle part in H. vittatus but in H. translucidens the teeth of the basibranchial plate are fewer and about eight in number (Fig. 5A). Hypobranchials (hyp). The hypobranchials (hyp) are three on either side, belonging to the first to third branchial arches. The hypobranchials decrease in length posteriorly. The first hypobranchial connects with the part between the first and the second basibranchials. The second hypobranchial connects with the posterior end of the second basibranchial. The third hypo branchials are connected with the both sides of the posterior narrow part of the

92 Yoshitaka Yabumoto and Teruya Uyeno third basibranchial (Fig. 5A). Ceratobranchials (cbr). There are five pairs of the ceratobranchials. The ceratobranchials are the longest bones in the branchial arches. They decrease in length and width posteriorly. The first to third ceratobranchials articulate anteriorly with hypobranchials. The anterior end of the fourth ceratobranchial extends partly as a process. The fourth ceratobranchial bears two rows of the gill rakers on the dorsal surface. The gill rakers of the inner row are smaller than those of the outer row. Other ceratobranchials bear a single row of the gill rakers. The fifth ceratobranchial is somewhat expanded near its base, and it bears the lower pharyngeal (pha lo) plate which has conical teeth along the posterior border. Four or five teeth are present on the lower pharyngeal plate. (Fig. 5A) Epibranchials (epb). Four epibranchials are present and decrease in size posteriorly. The processes of the epibranchials extend dorso-posteriorly and increase in length posteriorly. The third epibranchial bears two rows of the gill rakers. The other epibranchials bear a single row. Posteriorly the fourth epibranchial expands as a wing. The posterior part of the fourth epi branchial is narrower in H. translucidens than in H. vittatus. The upper pharyngeal (pha up) plate is round and lies on the anterior end of the fourth epibranchial. Three to six conical teeth are present on the anterior border of the plate. (Fig. 5A) Pharyngobranchials. There are three pairs of the pharyngobranchials. The pharyngobranchials decrease in length anteriorly. Each pharyngobranchial is narrow anteriorly and widens posteriorly. The second and third pharyngo branchials extend laterally the short processes for the epibranchials. Dorsally the first pharyngobranchial is attached to the ventral surface of the parasphenoid. Gill Rakers. The number of the gill rakers is 10 on the upper limb and 26 to 30 on the lower limb of the first branchial arch in H. vittatus. The number of the gill rakers is 8 on the upper limb and 22 to 24 on the lower limb in H. translucidens. One gill raker is present on the corner between the upper and lower limb in both species. The gill raker is slender and bears the minute teeth on the inner surface. All gill rakers have same feature (Fig. 5B). The double rows of the gill rakers are present on the third epibranchial and fourth ceratobranchial. The other ceratobranchials and epibranchials bear a single row of the gill rakers. Pectoral Girdle and Fin Supratemporal (supt). The paired supratemporals are present and have the anterior and dorsal limbs. The postero-ventral corner of the supratemporal, which forms a short bony tube for a sensory canal, is attached to the external surface of the posttemporal. The sensory canal from the postorbital opening of the supraorbital canal passes through the anterior limb of the supra-

Osteology of the Clupeiform fish, genus Hyperlophus (II) 93 temporal, which has a flange along its ventral edge adaxially, to the groove on the posttemporal (gpt). The dorsal limb of the supratemporal bears a flange along its anterior edge overhanging the sensorycanal from a groove of the parietal which meets the sensory canal from the postorbital opening of the supraorbital canal at the medial part of the supratemporal (Fig. 5G). Posttemporal (pot). The main body of the posttemporal is represented by a broad plate of the bone which bears the flangeoverhanging the groove for the sensory canal (gpt) along near its antero-ventral edge. There are two processes on the posttemporal. The dorsal flat process of the posttemporal (pre) attaches to the epiotic and parietal. The ventral process arising from the ventral surface of the main body firmly attaches to the intercalar. The flange of the groove for the sensory canal on the posttemporal (gpt) forms a narrow bony bridge at the anterior end. Two openings are present on the base of the flange for the sensory canal. In H. vittatus four or five indistinct pores are present near the anterior end of the groove wall. In H. translucidens these are absent (Fig. 5G). Cleithrum (cle). The cleithrum is a long bone and curves anteroventrally. The dorsal end of the cleithrum is acuminate. The ventral end connects with the opposite cleithrum. The anterior rim of the cleithrum turns inward and forms a bony plate which forms the postero-lateral wall of the gill chamber. The dorsal end of the scapula is attached to the ridge on the inner sur face of the posterior bony sheet of the cleithrum. The plate-like process beneath the ridge for the scapula is in contact with the mesocoracoid. The small bony sheet extends posteriorly from the bony plate of the anterior rim and is attached to the antero-dorsal corner of the coracoid on the external surface. The long ridge lies on the middle part along the anterior rim of the cleithrum. The dorsal one-third of the cleithrum articulates with the supracleithrum (Fig. 5G). Postcleithra (poc). There are two slender postcleithra. The dorsal end of the upper postcleithrum (poc up) is broad and is attached to the inner surface of the ventral part of the supracleithrum. The ventral half of the upper post cleithrum is attached to the lower bone (poc lo). The lower postcleithrum is as long as the upper bone. The ventral end of the lower postcleithrum reaches to the eighth ventral scute in H. vittatus. It reaches to the seventh ventral scute in H. translucidens. Each ventral scute in both species is the anterior first of the deep scute (Fig. 1 and 5G). Scapula (scap). The scapula is a stout element and lies between the cleithrum and the coracoid as a bridge. Some anterior actinosts articulates with the scapula. Dorsally the scapula is attached to the inner surface ofthe cleithrum. Ventrally the scapula is separated from the coracoid by a narrow strip ofcartilage. The anterior two actinosts articulate with the scapula in H. vittatus. The anterior three actinosts articulate with the bone in H. translucidens (Fig. 5G). Mesocoracoid (mes). The mesocoracoid is a slender cylindrical bone.

94 Yoshitaka Yabumoto and Teruya Uyeno The ventral end of the bone is attached to the scapula and coracoid. The dorsal end is attached to the process of the cleithrum. The mesocoracoid forms a bridge between the cleithrum and the coracoid (Fig. 5G). Coracoid (era). The coracoid is broad and curves inward as a wing. The connecting part of the coracoid with the scapula is thick. The ridge runs antero-ventrally on the external surface of the coracoid from this connecting part. The dorso-posterior corner of the coracoid is thick, as a stout process, and articulates with the fourth actinost. The short triangular process raises on the inner surface of the coracoid before the connecting part with the scapula and is attached to the mesocoracoid. The anterior margin of the coracoid is in contact with the cleithrum. The slender posterior process of the coracoid extends backward (Fig. 5G). Actinosts (act). There are four pectoral actinosts. The first actinost (act 1) is largest and broadest. The other actinosts are slender and somewhat same in size. The ventral ends of the first to third actinosts are forked. The anterior two actinosts articulate with the cartilage between the scapula and the coracoid in H. vittatus. The anterior three actinosts articulate with the scapula in H. translucidens. The forth actinost articulates with the coracoid in both species. In H. vittatus, the first actinost has five small ossicles and articulates with the second to seventh pectoral fin rays, the second actinost has one small ossicle and articulates with the eighth to tenth rays, and the third and forth actinosts have one small ossicle and articulate with the eleventh rays. In H. translucidens the first actinost has three small ossicles and articulates with the second to fifth pectoral fin rays, the second actinost has two small ossicles and articulates with the sixth to eighth rays. The third actinost has one small ossicle, the fourth actinost has no ossicle, and the third and fourth actinosts articulate with the ninth to twelfth rays. The number of the ossicles on each actinost is different in specimen respectively. The dorsalmost pectoral fin ray articulates directly with the scapula (Fig. 5G). Pelvic Girdle The pelvic girdle consists a paired basipterygium (bap). The basipterygium is selender anteriorly. Posteriorly the basipterygium is deep and broad. The basipterygium meets its fellow at the midline near the posterior end. The posteroventral stout process is separated widely from its mate of opposite side by a catilage. Each basipterygium is met mutually at midline on the dorsal surface. The dorsal meeting portion of the basipterygiums is longer in H. vittatus than in H. trans lucidens. The posterior process of the basipterygium is longer in H. vittatus than in H. translucidens. The pelvic fin rays are seven in number. Four small pterigyophores (ptr 1-4) articulate with the depressions on the posterior margin of the basipterygium respectively. The first pterygiophore (ptr 1) articulates

Osteology of the Clupeiform fish, genus Hyperlophus (II) 95 with the upper branchof the anterior end of the first pelvic fin (P2f). The lower branch of the first pelvic fin ray at the anterior end curves under the basipteryg ium and reaches near the midline. The second pterygiophore (ptr 2) articulates with the upper branches of the second to fourth pelvic fin rays. The third bone (ptr 3) articulates with the upper branches of the fifth to seventh pelvic fin rays. The fourth bone (ptr 4) articulates with the lower branch of the seventh pelvic ray. The ridge lies on the dorsal surface of the fourth pterygiophore (Fig. 5D). Vertebral Column The vertebral column is composed of 39 to 40 vertebrae including the first preural centrum. Of these, 21 to 22 are abdominal vertebrae and 18 are caudal vertebrae in H. translucidens. In H. vittatus the vertebral column is composed of46 to 48 vertebrae including the first preural centrum. Of these, 29 to 31 are abdom inal vertebrae, and 16 to 18 are caudal vertebrae. In the specimens of//, vittatus (KMNH VR 100,089) the ribs of the 30th vertebra are considerably small. The left and right neural spines of the anterior vertebrae are not fused. In H. vittatus the anterior 23 and 25 neural spines are forked. In H. translucidens the anterior 19 neural spines are forked. All of the neural spines are curved smoothly and extends dorso-posteriorly. The last four neural spines of the caudal vertebrae are longer than the others and support the caudal scute and vestigial rays. The haemal spines are similar in both speciese. The last four haemal spines are slightly wider than the others and support the caudal scute and vestigial rays. The haemal spine of the first preural centrum bears a bony flange on the anterior margin (Fig. 1). Vertebrae. Dorsally the centra bear neural arches which are deeper cranially, and become wider and lower caudally. The neural arch of the first centra has no neural spines. About first 20 neural arches are not ossified with the centra and the other neural arches are fused with the centra in H. vittatus. About first 14 neural arches are not ossified with the centra in H. translucidens. The neural arches bear anteriorly directed projection, dorsal prezygapophyses, which are slender. The centra bear the dorsal postzygapophyses on the posterior end of the dorsal surface. The postzygapophyses in the anterior region are slender and in the posterior region are broader. The last four neural arches are broadest and fused with the whole dorsal surfaces of the centra. The centra bear paired ventral transverse processes, parapophyses, which are attached near the antero-ventral corners of the centra. The parapophyses except the first and second parapohyses support the ribs. The parapophyses are smaller anteriorly and increase in length behind these anterior 16 to 19 centra in H. vittatus. The parapophyses increase in length behind these anterior 14 centra in H. translucidens. The transverse bony bridge connects the parapophyses

96 Yoshitaka Yabumoto and Teruya Uyeno in each of the 3 or 4 most posterior abdominal centrum, thus forming a close haemal arch on each centrum as a H-shaped in H. vittatus. Two posterior abdominal centra form a close haemal arch in H. translucidens. The para pophyses of the 3 or 4 most posterior abdominal centra have the ventral prezygapophyses on the anterior margin near the bases in H. vittatus. The parapophyses of the 5 most posterior abdominal centra have the ventral prezygapophyses in H. translucidens. The ventral postzygapophyses are raised on the 6 most posterior abdominal centra in H. vittatus. They are raised on the 3 most posterior abdominal centra in H. translucidens. The last 5 or 6 haemal arches of the caudal centra with paired openings are broad and fused the whole dorsal surface of the centra (Fig. 1). Epineurals. The anterior end of the first paired epineural lies on the second vertebra in H. vittatus. The anterior end ofthe last bone lies on the anterior end of the first preural centrum. The anterior end of the first paired epineural lies on the fourth vertebra in H. translucidens. There are 43 to 45 epineurals and 12 to 13 bones beneath the dorsal pterygiophores are forked posteriorly in H. vittatus. There are 35 epineurals and four bones are forked posteriorly in H. translucidens. In both species some epineurals of the caudal part are forked anteriorly. The anterior ends of the epineurals of the caudal part increase posteriorly in width (Fig. 1). Epipleurals. The anterior end of the first epipleural lies on the 17th rib in both species. The last epipleural is present parallel to the perhypural in the lateral muscle in both species. The widths of the epipleurals increase posteriorly. The epipleurals of abdomen are very short. Three bones above the anterior anal pterygiophores are forked (Fig. 1). Epicentrals. The epicentrals are short bones. The first pair of epicentrals is attached to the first vertebra. There are 25 pairs of the epicentrals in H. vittatus. There are 19 pairs of the bones in H. translucidens. Ribs. The first pair of ribs is attached to the third vertebra. Ventrally the first rib reaches to the first long ventral scute. The last rib lies on the first anal pterygiophore without contact. There are 21 pairs of ribs in H. vittatus. There are 19 pairs in H. translucidens. Interneurals. There are 15 to 16 interneurals in H. vittatus, and 12 in H. translucidens. The first interneural is situated beneath between the third and the fourth dorsal scutes and inserted between the posterior wall of the cranium and the first neural spine. The second interneural is situated between the fourth and fifth dorsal scutes and inserted between the first and the second neuralspines. The other posterior interneurals are situated at equal spaces respectively (Fig. 1). Caudal rays and skeleton The branched rays of the caudal fin are 17, with a long unbranched above

Osteology of the Clupeiform fish, genus Hyperlophus (II) 97 and another one below. Eight to ten vestigial rays are in front of each of the long unbranched rays. A caudal scute is present above the dorsal end of the neural spine and another one is present below the ventral end of the haemal spine of the fifth preural centrum. In the lateral view, the eighth and ninth branched rays are forked at the anterior parts. The upper long branch of the eighth branched ray extends anteriorly over the center of the second hypural. The lower long branch of the ninth branched ray extends anteriorly over the center of the third hypural (Fig. 1). The parhypural (parh) is attached with the first preural centrum (preu 1) and extends postero-ventrally. The hypuropophysis of the parhypural (hpap) extends postero-ventrally from the anterior end of the parhypural and reaches to anterior one-third of the parhypural (Fig. 5H). The six hypurals (hyu 1-6) are separated from each other. The first and third hypurals are largest. The first hypural is separated from the first preural centrum. There is a small unossified patch on the first hypural near center. The second hypural is a slender bone and attached to the first ural centrum (v ura 1). There is a small unossified patch on the center of the second hypural. The third hypural is similar in size of the first hypural. The upper half of the third hypural is slightly thick. The fourth to sixth hypurals are cylindrical and decrease in length dorsally. The anterior end of forth and fifth hypurals are covered by the second uroneural (urn 2). The sixth hypural is slightlyseparated from the second uroneural. The neural arch is raised on the dorsal surface of the first preural centrum and extends along the first uroneural. The first preural centrum is slender posteriorly. The ventral surface of the first preural centrum is attached with the parhypural and is separated from the first hypural (hyu 1). The posterior end of first preural centrum is slightly separated from the first ural centrum (v ura 1) (Fig. 5H). The ural centra (v ura) are two in number. The first ural centrum (v ura 1) is larger than the second bone (v ura 2). The ventral surface of the first ural centrum is attached with the second hypural. The ventral surface of the second ural centrum is attached to the third hypural. The dorso-posterior corner of the second ural centrum is covered by the anterior ends of the paired second uroneurals (Fig. 5H). There are three pairs of uroneurals (urn). The first uroneural (urn 1) is fused with the first preural centrum and extends dorso-posteriorly and reaches to the level of the sixth hypural. The second uroneurals (urn 2) cover the dorsoposterior corner of the second uroneural (urn 2) at the anterior ends and extend dorso-posteriorly to the level of the sixth hypural. The third uroneural (urn 3) is a short twisted bone. The bones (urn 3) cover the dorsal end of the first and second uroneurals (urn 1-2) and extend posteriorly over the sixth hypural. The posteriorends of the third uroneurals meet mutually (Fig. 5H). The epurals are slender and slightly decrease in length posteriorly. The

98 Yoshitaka Yabumoto and Teruya Uyeno epurals lie between the neural spine of the second preural centrum and the first uroneurals. The length of epurals are less than the one-third of the haemal spine of the second preural centrum. The neural spine of the second preural centrum is same in shape as those of the other centrum. Its haemal spine bears a bony flange along the anterior margin of the bone (Fig. 5H). Dorsal Fin The dorsal fin is situated in the center of the back and is composed of 15 or 16 fin rays which are segmented. The lepidotrichs are supported by 15 or 16 pterygiophores, each composed of proximal, median, and distal elements. The number of the pterygiophores of the dorsal fin equals with dorsal fin rays. The distal pterygiophore is small and is clasped between the base of each paired ray. The first proximal pterygiophore is considerably larger than those succeed ing it, and it expands anteriorly as a fan. The ventral end of the first ptery giophore reaches to the dorsal end of the haemal spine of the 17th centrum. The dorsal margin of the first pterygiophore is expanded laterally at the posterior end with the pair of the small foramina. The first pterygiophore bears the ridge along its posterior margin. Four dorsal scutes lie on the dorsal margin of the first pterygiophore in H. vittatus. Three dorsal scutes lie on the bone in H. translucidens. The proximal pterygiophore is expanded dorsally and bears the ridge throughout its length. The middle proximal and median pterygiophores are separated by a cartilage in H. vittatus. In H. translucidens all proximal and medi an pterygiophores are fused. The ventral ends of the proximal pterygiophores are separated from the neural spines in H. vittatus. In H. translucidens they are inserted between the forked neural spines. The last pterygiophore is a small bony plate and slightly extends posteriorly (Fig. 5E). Anal Fin The origin of the anal fin isat midway between the pelvic fin and the caudal peduncle. In H. vittatus theanalfin is composed of19 to 20fin rays and the ptery giophores oftheanal fin are 18 to 19 in number. In H. translucidens theanal fin is composed 20 fin rays and the pterygiophore are 19 in number. There are one fewer pterygiophore than anal fin. All of the proximal and median pterygio phores are fused in both species. Thedistal pterygiophore is small and is clasped between the base of each paired ray. The pterygiophores of the anal fin are slender and are expanded ventrally. The anterior two or three pterygiophores bear the bony flanges anteriorlyand posteriorly. The first pterygiophore is largest and is articulated with the first and second anal fin rays. The first pterygiophore is somewhat straight in H. vittatus. It is curved in H. translucidens. The dorsal ends of the pterygiophores are separated from the haemal spines in H. vittatus.

Osteology of the Clupeiform fish, genus Hyperlophus (II) 99 In H. translucidens they are inserted between haemal spines. In both species the last pterygiophore is a small bone, without antero-dorsal extension (Fig. 5F). Dorsal Scutes There are 26 dorsal scutes in H. vittatus and 17 in H. translucidens. The first dorsal scute is different in shape from the other posterior scutes (Fig. 4C, F). The first dorsal scute is somewhat round and pointed at postero-medial and postero-lateral ends, and has a small notch on the anterior margin at midline in H. vittatus. The length of the first dorsal scute is longer than its width in H. vittatus. The first dorsal scute is concave at the anterior margin and has a notch on the posterior margin at midline in H. translucidens. The width of the first dorsal scute is greater than its length in H. translucidens. The dorsal scutes excepting the first one are pointed at both ends. Thekeel on the dorsal scute excepting the first scute is higher in H. translucidens than in H. vittatus. The dorsal scutes are wider in H. translucidens than in H. vittatus. The widths of the dorsal scutes are about one-second oftheir lengths in H. translucidens. Their widths are about one-third of their lengths in H. vittatus (Fig. 4C, F). Ventral Scutes The anterior small ventral scutes are similar in shape to the dorsal scutes. The anterior small ventral scutes are slightly wider than the dorsal scutes. The keels on the anterior smallventral scutes are lower than the dorsalscutes. There are 5 to 7 anterior small ventral scutes in H. vittatus. There are 6 to 7 in H. translucidens. The first long ventral scute lies beneath the first rib. The posterior margin of the ventral scute before the pelvic fin is concave for the base ofthe pelvic fins. There is a small ventral scute under the pelvic fin base. There are 14 to 17 long ventral scutes before the pelvic fin, and 11 to 12 behind the pelvic fin in H. vittatus. There are 10 to 12, and 7 to 8 in H. translucidens. Remarks Hyperlophus, which is distributed in Australia and considered to be one of the most primitive clupeid genera, has two species. They are H. vittatus and translucidens, and here osteologically described and compared. H. vittatus is slender and generally considered to have more primitive characters, and H. translucidens has higher head and body and considered to possess more derived characters. Though the number of specimens available were limited, here we sum marize differences which appear to be important. 1) In the neurocranim, the width is equal to the depth in H. vittatus, but in H. translucidens the width is slightly shorter than the depth. The orbital space is

100 Yoshitaka Yabumoto and Teruya Uyeno larger in H. translucidens. 2) The anterior part of the ethmoid is deeper in H. translucidens than in H. vittatus. 3) The head of the prevomer is broader in H. translucidens than in H. vittatus. In H. translucidens the posterior part of the prevomer becomes narrower and the constriction is present between the prevomer and parasphenoid in the ventral view. In H. vittatus the posterior part of the prevomer gradually becomes narrower and the constriction is absent. 4) The interorbital septum of the orbitosphenoid anteriorly sutures with the prefrontals in H. translucidens, but it isseparated from the prefrontals by a catilage in H. vittatus. 5) The dorsal end of the pterotic is separated from the parietal by the large catilage, or partly overlapped by the parietal in H. vittatus, but it isoverlapped by the parietal in H. translucidens. The round swelling on the dorso-medial part of the pterotic is larger in H. translucidens than in H. vittatus. 6) The inner margin of the epiotic is overlied by the exoccipital in H. trans lucidens, but in H. vittatus the epiotic is separated from the exoccipital by a cartilage. In the lateral view, the anterior margin of the epiotic overlies the pterotic in H. translucidens, but the anterior margin of the epiotic is ventrally in contact with the pterotic by a narrow strip of cartilage in H. vittatus. 7) The swelling for the ventral part of the posterior vertical semicircular canal is formed by the pterotic, exoccipital, and epiotic in H. vittatus. This swelling is formed by the exoccipital and epiotic in H. translucidens. 8) In the posterior view the ventral margin of the supraoccipital is round and separated from exoccipitals by a cartilage in H. vittatus, but in H. translucidens the ventral margin of the supraoccipital is not round and runs parallel to the dorsal margin of the exoccipitals. 9) The articulated part of the parasphenoid for the upper pharyngeals forms a notable ridge in H. translucidens, but in H. vittatus the articulated part forms a low ridge. 10) The antero-dorsal apex of the quadrate is in acute angle in H. vittatus, but it is nearly at right angle in H. translucidens. 11) The dentary teeth are larger in H. vittatus than in H. translucidens. 12) The teeth of the maxillary are smaller inh. translucidens than in H. vittatus. In H. vittatus the posterior wing of the maxillary bears five or six rows of the teeth on the external surface, but in H. translucidens the teeth are very minute and the tooth rows are indistinct. 13) In H. translucidens the head of the hyomandibular is divided into the ex panded anterior (ace) and posterior parts (pec), but in H. vittatus the expanded anterior and posterior ends of the head are connected mutually. The anteroventral wing ofthe hyomandibular is larger in H. translucidens than in H. vittatus.