New Mayflies from the Upper Mesozoic Transbaikalian Locality Chernovskie Kopi (lnsecta: Ephemerida = Ephemeroptera)

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1 Paleontologcal Journal, Vol. 34, No. J, 2000, pp Tronslaledfrom Paleontologcheskl Zlum1al, No. 1, 2000, pp Orgnal ftussan Text Copyrght e 2000 by Sntshenkova. Englsh Translaton Copyrght e 2000 by MAK "Naukallnterperodca" (Russa). New Mayfles from the Upper Mesozoc Transbakalan Localty Chernovske Kop (lnsecta: Ephemerda = Ephemeroptera) N. D. Snltshenkova Paleontologcal nsttute, Russan Academy of Scences, ul. Profsoyuznaya 123, Moscow, Russa Receved June 8, 1998 Abstrad-Seven new spec~s ard a new genus, Clavneta transbakalca sp. nov., C. ctma sp. nov., Mesoneta deusta sp. nov. (Mesonetdae), Sberogentes rectcostals sp. nov. (Hexagentdae), Mesobaets amplectus sp. nov., Sphangarus rotundus gen. et sp. nov., and Stackelbergsca clara sp. nov. (Sphlonurdae), are descrbed based on nymphs. The mayfly assemblage of the Transbakalan localty Chemovske Kop s analyzed. Ths assemblage s unque for the Mesozoc of Asa, but generally more smlar to Jurassc rather than to Cretaceous assemblages. NTRODUCTON The materal descrbed below came from the localty Chemovske Kop (Chta Regon, Chta Dstrct, Chta-ngoda Depresson, the left bank of the ngoda Rver, km southwest of Chta) that was brefly characterzed elsewhere (Sntshenkova, 1998). All the mpressons but one were collected by S.M. Sntsa from Outcrop 9, beds 1, 2, 3, 10, and 16 (hereafter 911, 912 etc. respectvely). One mpresson (no. 4626/252) was found by N. Berdnkov n Outcrop 1006/3. All mayfly specmens are represented by larval mpres-. sons on burned mudstone. The organc matter was not preserved because of fre, and some characters are obscure. Moreover, the vast majorty of remans are ncomplete. Nevertheless, the materal n queston s of great nterest. The materal studed, ncludng the types, s housed n the co11ecton of the Paleontologcal nsttute of the Russan Academy of Scences (PN). RESULTS AND DSCUSSON Only 39 of 56 specmens were dentfed at speces level. They belong to seven speces of seven genera, whch may be allocated to the famles Sphlonurdae (Mesobaets amplectus sp. nov., Stacke/bergsca clara sp. nov., Sphangarus rotundus gen. et sp. nov.), Hexagentdae (Sberogentes rectcostals sp. nov.), and Mesonetdae (Mesoneta deusta sp. nov., Clavneta ctma sp. nov., C. transbakalca sp. nov.). Specmen no. 4626/238, an mpresson of a nymph from Outcrop 9/16, was dentfed as Proameletus (Sphlonurdae). t s mpossble to dentfy ths speces precsely because of poor preservaton of the specmen that s represented by ncomplete remans of the abdomen wth tal flaments. The specmen dffers from the only known speces P. caudatus Sntsh. (Sntshenkova, 1976) n the narrower abdomnal segments. Sxteen specmens of mayfles are not dentfed wth greater precson. The mayfty fauna of Chemovske Kop may apparently be consdered as a sngle assemblage, although there may be dfferences between dfferent beds that cannot be recognzed because of nsuffcently preserved materal. For nstance, two specmens of S. rectcostals sp. nov. come from the same bed 9/3, where none of M. deusta sp. nov. appear, although the latter are found n beds 911, 912, 9/10, and 9/16. The fauna of the localty s pecular n many aspects. Unlke any other Mesozoc fauna t shows hgh taxonomc dversty, an unusual generc fauna, and domnant taxa. Chemovske Kop exceeds any other Mesozoc localty n Asa n the absolute number of speces (eght) and genera (eght) found, although consderably more remans have been collected n many stes. n the Jurassc deposts mayfles are represented by three to four speces of two or three genera (Sntshenkova, 1985), whle only one speces of the genus Ephemeropss s recorded n the majorty of the Lower Cretaceous localtes. The only excepton s the localty Hutel-Hara n southeastern Mongola (Tsagaan-Tsav Formaton, the Upper Jurassc-Lower Cretaceous) where fve speces of fve genera belongng to fve famles have been dscovered (Sntshenkova, 1989). Nevertheless, ths localty shows lesser generc and speces dversty compared to Chemovske Kop. There s only one Lower Cretaceous localty outsde Asa, n Brazl (Santana), wth a more dverse mayfly fauna than n Chemovske Kop. Not less than 11 speces n 11 genera of nne famles are recorded from there (McCafferty, 1990; Martll, 1993). All famles represented n Chemovske Kop, vz. the Sphlonurdae, Hexagentdae, and Mesonetdae, are usual n Mesozoc assemblages n Asa. Fossoral mayfles and Epeorommdae found n some other localtes are not recorded. All genera except for endemc Sphangarus gen. nov. have prevously been

2 ty >argh at re- ~cre er ts C ~s y e 0, _ t.. ' recorded n the Asan Mesozoc, and some of them are wdespread. However, ther assocatons are unque. Both genera Mesobaets and Meso11eta are found n many Jurassc localtes, but ther assocaton wth Sberoge11tes s recorded only n Novospasskoe (Buryatya, the lchetu Formaton) and Oshn-Boro Udzuur-Uul (Western Mongola, the Jargalant Formaton) (Sntshenkova, 1985, 1991), whereas Stackelbergsca, C/avneta, and Proameletus have not prevously been recorded n assocaton or wth any of above genera (Sntshenkova, 1985, 1989, l 990a). All the speces found n Chemovske Kop are endemc. The pattern of domnaton s also unque. Three of the most abundant speces are represented by nearly equal numbers of specmens,.e. 12 specmens of S. rottmdus gen. et sp. nov., 11 specmens of S. clara sp. nov., and 0 specmens of M. deusta sp. nov. The speces S. rectcostals sp. nov. and M. amp/ectus sp. nov. are represented n the collecton by two ndvduals, and Proameletus sp. and both speces of Clavneta are represented by a sngle ndvdual each. n other localtes speces of Mesobaets and Proameletus are always among the domnants. Although sphlonurds often domnate by the number of ndvduals n Mesozoc faunas, they are usually represented by a sngle genus wth one or two speces, whereas n Chernovske Kop two speces of two genera are recorded n equal proportons. Mayfles of the famly Hexagentdae often domnate n the Lower Cretaceous beds (Sntshenkova, 1986, l 990b; Mccafferty, 1990), except for a few occurrences, e.g., the Koonwarra Localty n Australa (Jell and Duncan, 1986). Snce Chernovske Kop s stuated n the regon where many other Mesozoc mayfly localtes have been dscovered, the pecularty of the mayfly fauna may be explaned by ether taphonomc, or ecologcal, or stratgraphc reasons. The majorty of the speces found apparently developed n the same lake where the nsect-bearng sedments were deposted. Thus these speces are autochthonous n a broad sense. t s true for the most common speces mentoned above as well as for M. amplectus sp. nov., Proameletus sp., S. rectcostals sp. nov., whch are superfcally smlar to other lmnetc speces and belong to genera found n other lacustrne deposts. The small quantty of ther remans may be explaned by ether a low number of the nsects or ther preference for other parts of the lake. Smlar to nymphs of both Clavneta speces, they mght be allochthonous and have been transported here from flowng water bodes. Ther morphologcal features are not characterstc of mayfles from stagnant water and ndcate a possble flter-feedng det. However, fltrators need flowng water wth seston. Hence, the bural of Chernovske Kop does not dffer taphonomcally from the majorty of others burals n Transbakala and Mongola. The fact that nymphs are found n the beds contanng leaf and seed floras may explan ecologcal reasons PALEONTOLOGCAL JOURNAL Vol. 34 No NEW MAYFLES 69 for the pecularty of the mayfly assemblage from Chernovske Kop. Mayfles remans are accompaned by numerous plant remans. Only few Jurassc localtes n the regon of lake Bakal (Cheremkhovo Formaton) and western Mongola (Jargalant Formaton) resemble Chernovske Kop n ths respect. t s noteworthy that Mesobaets, Mesoneta, and Sberogentes are recorded together n the deposts of the Jargalant Formaton as well. n contrast, n Transbakala, n central and western Mongola nearly all burals occur n beds where the macroremans of plants are much scarcer. Only n the deposts of the Bukachacha Formaton, the Bukachacha Localty, nymphs of hexantd Ephemeropss were found drectly n coal measures (Sntshenkova, 1990a). Snce plant detrtus, both large- and smallszed, s the man det of nymphs of many mayfles, ts abundance and composton nfluence the fauna sgnfcantly. Hence, the pecularty of the mayfly assemblage of Chemovske Kop may at least partly be explaned by ths. The large amount of plant debrs may nfluence the fauna ndrectly, through the presumable bactercdal effect of Mesozoc plants. Exstence of so-called hypotrophc lake ecosystems n the Mesozoc s supposed be connected wth such an effect (Zherkhn and Kalugna, 1985; Sntshenkova, 983; Sntshenkova and Zherkhn, 1996). The man source of ths debrs are gngoaceous plants. t s of great nterest, n ths respect, that these plants are poorly represented n the Jurassc nsectbearng beds (Zherkhn and Kalugna, 985); and Lower Cretaceous nsects have been known manly from the deposts of large lakes whch were not affected strongly by hypotrophc condtons (Zherkhn and Kalugna, 1985; Sntshenkova and Zherkhn, 1996). The hgh dversty of mayfles may reflect consderable oxygenaton of water body. All presumed autochthonous nymphs found n Chernovske Kop are benthc detrvores judgng from ther morphologcal features. There are two groups among them, vz. wth large glls, Sberogentes, and wth small glls whch comprse all the others genera. Fossoral forms are absent. Such a set of morphoecotypes generally resembles the assemblage whch s characterstc for the Jurassc hypotrophc lakes of southern Sbera, but the forms wth large glls, manly the Epeorommdae, are often more abundant n those lakes. The causes for the relatve abundance of smalland large-glled nymphs n dfferent assemblages are not yet clear. Presumably allochthonous nymphs of Clavneta have long and dense setaton of the fore legs, a characterstc of recent flter-feeders, and consequently may be referred to ths type. The age of the localty Chernovske Kop s dsputable (Sntshenkova, 1998). t s possble to compare the fauna wth other assemblages only at generc level snce all the speces of the mayfles are endemc. All the genera, except for the endemc Sphangarus gen. nov., have been known from ether Jurassc or debatable

3 .. 70 SNTSHENKOV A Explanaton of Plate 11 Fg. 1. Clavneta transbakalca Sntshenkova, sp. nov.; holotype PN, no. 4626/200, x5.3. Fg. 2. Clavneta ctma sp. nov. Sntshenkova. sp. nov.; holotype PN, no. 4626/252, xo. Fg. 3. Mesoneta deusta Sntshenkova. sp. nov.; holotype, PN, no. 4626/244, xl2. Fg. 4. Sberogentes rectcostals Sntshenkova, sp. nov.; holotype PN, no. 4626/221, x6.3. Fg. 5. Mesobaets amplectus Sntshenkova, sp. nov.; holotype, PN, no. 4626/201, x6. Fg. 6. Stackelbergsca clara Sntshenkova, sp. nov.; holotype PN, no. 4626/232, x8.6. Fg. 7. Sphangarus rotundus Sntshenkova, gen. et sp. nov.; holotype PN, 4626/202 x4. Jurassc or Cretaceous beds. Mesobaets and Mesoneta are characterstc mostly for the faunas of the Early and Mddle Jurassc. n the younger assemblages they are rttre and represented by much larger speces (Sntshen 4ova, 1989). The speces of Mesoneta and Mesobaets from Chernovske Kop are small and resemble the ~arly-md Jurassc ones. n contrast, representatves of t~e genus Stackelbergsca were found n large numbers o ly n the Upper Jurassc of Transbakala whereas t ey are qute rare n the older beds (Sntshenkova, 1 91). The genus Clavneta has been known untl now ottly from the Localty of Shara-Teg n western Mongol'- (Sntshenkova, 1991). nsect-bearng deposts of Sl\ara-Teg may most lkely be referred to the Upper J~rassc, although the Lower Cretaceous can not be e~ctuded wth certanty. Besdes the Lower-Mddle Jurassc, Sberogentes are found n the Tsagaan-Tsav F~rmaton n southeastern Mongola whch s consder~d as the basalmost Lower Cretaceous (Sntshenkov, 1989). And fnally, the genus Proameletus has be n known untl the present only from the Glushkovo Fohnaton and ts analogues n eastern Transbakala, the. age of whch s estmated to be the Late Jurassc to Al~an (Sntshenkova, l 990a). n those beds Proamelet1* s nearly always recorded together wth the genus Furvoneta whch s absent from Chernovske Kop. To summarze, the general appearance of the mayfly assemblage of Chernovske Kop testfes to a Jurassc, probably Late Jurassc, age although ts pecularty makes ts comparson wth other faunas dffcult. Such a datng agrees wth the data obtaned from the other aquatc nsects, the stonefles (Sntshenkova, 1988). SYSTEMATC PALEONTOLOGY Famly Mesonetdae Tshemova, 1969 Genus Clavneta Sntshenkova, 1991 Cla11neta transbakalca Slnltshenkova, sp. nov. Plate 11, fg. l E t y m o o g y. From Transbakala. Ho 1 o type. PN, no , anteror part of nymph body; localty Chernovske Kop, outcrop 9/1; Upper Jurassc. De scrpt on (Fg. la). Nymph. The head s elongate and lttle narrowed anterorly, ts length s almost 1.5 tmes greater than ts wdth at the.hnd margn. The maxllary palps have two short basal segments and the long apcal one s densely covered wth long hars, the palps are protrudng from the head sdes. The ' :. r --~ ( F: 1. Nymphs of mayfles of the famly Mesonetdae: (a) Clavneta transbacalca sp. nov., holotype PN, no ; (b) C. ctma sp. nov., holotype PN, no. 4626/252; (c) Mesoneta deusta sp. nov., holotype PN, no. 4626/244. Scale bar mm. PALEONTOLOGCAL JOURNAL Vol. 34 No (c) J,, fta,, :~.

4 d s h s narents ong The NEW MAYFLES 71 Plate 11 p. To ayfly rassc larty Such orher 8). t of 911; PALEONTOLOGCAL JOURNAL Vol. 34 No. 2000

5 72 SNTSHENKOVA pronotum s transverse, 3.2 tmes as wde as long, and 0.4 tmes the length of the head. The wng sheaths are narrow and close to each other. The fore femora are twce as wde but tmes the length of the tbae. There are long hars, not n fasccles, along the nner sde of the femora and tbae. Measurements (mm): thelength of the mpresson s 6.6, the complete length of the nymph body s approxmately 13. C o mp a r s o n. Dffers from C. cantabls Sntsh., 1991 n that the head and fore tbae are longer, and n the smatler sze. Rem ark s. The genus Clavneta was orgnally descrbed n the famly Leptophlebdae, where t was placed close to Furvoneta Sntsh. based on the smlarty of the gll structure (Sntshenkova, 1991). The recent revson of fossl mayfles showed that the genus Furvoneta and the genus Mesoneta Br., Redtb. et Ganglb., closely smlar to Furvoneta, are not related to the Leptophlebdae and should be assgned to the superfamly Sphlonurodea (Kluge, 1993). Clavneta dffers substantally from the genus Colocrus McCaff. (Olgoneurdae) from the Lower Cretaceous of Brazl (Mccafferty, 1990) n the more prmtve structure of the flterng apparatus, Clavneta has dense hars on the fore f emora and tbae along ther nner sde rather than arranged n broad fasccle lke n olgoneurds. t s known that typcal morphologcal features of larvae, the presence of long hars on the nner sde of the fore femora and tbae connected wth a flter-feedng det, appear among varous mayfly groups (Olgoneurdae, Behnngdae, Heptagendae, sonychdae) that are not always phylogenetcally close. A nearly complete nymph of the stonefly Trangulperla volucrs Sntsh., 1998 (no. 4626/237) s preserved besdes the mpresson of the mayfly. M ate r al. The holotype. Clavneta clma Snltshenkova, sp. nov. Plate 11, fg. 2 Et y mo o g y. From Latn ctmus (proxmate). 1 Ho lot y p e. PN, no. 4626/252, almost complete! you~g nymph {part and counterpart); Ch~movske \Kopt Localty, outcrop 1006/3; Upper Jurassc. Descrpton (Fg. lb). Nymph. The head s 1rounded, a lttle narrower and twce as long as the 1pronotum. The pronotum has beveled hnd angles; the \front angles are wdely rounded and somewhat prompent. Wng sheaths are short. Abdomnal segments have ~hort ndentatons on the latero-posteror poston. The abdomnal segments are tmes as wde as long. fhe glls have thckened outer and nner margns. The l~ngth of each glt does not exceed the wdth of a segrpent. Tal flaments are half as long as the body length. : 1 Measurements (mm): body length 5, the length df the tal flament 2.5. C o mp a r s o n. Dffers from known speces n the s~ape of the pronotum and smaller sze. R e mark s. The fore legs wth characterstc setaton are not preserved, but the glls wth typcal Clavneta-type structure allow referal of C. ctma to ths genus. Furvoneta has glls of smlar structure, but ts representatves are characterzed by wde abdomnal segments and long ndentatons latero-posterorly. These features are absent from the new speces. M a t e r a l. The holotype. Genus Mesoneta Brauer, Redtenbacher et Ganglbauer, 1889 Mesoneta deusta Slnltshenkova, sp. nov. Plate 11, fg. 3 Etymology. From Latn deustus (burnt). Ho 1 o type. PN, no. 4626/244, part and counterpart of the nymph wthout the tp of the abdomen; Chernovske Kop Localty, outcrop 9116; Upper Jurassc. Des c rp t on (Fg. le). Nymph. The head s oval shaped, prognathous, and twce as long as the pronotum. The pronotum s short, three tmes as wde as long. The body s approxmately 3.4 tmes as long as the abdomen s wde. The abdomen s three tmes as long as thorax and nearly twce as long as wde. The wdth of segments n the mddle part of the abdomen s 3.5 tmes ther length. Meas u rem en ts (mm): the holotype length 6.9, the full length of the nymph approxmately 8. C o m p a r s o n. The new speces s close to M. utrculata Sntsh., 1985 n sze and abdomnal segment wdth, but dffers n the shorter body.. Re marks. Up to now all speces of Mesoneta have been found n the Jurassc localtes of Sbera and Mongola: M. antqua Br., Redtb. et Ganglb., 1889 (Abashevo, Osnovka, Cheremkhovo, chetu, and Jargalant Formatons, the Lower-Mddle Jurassc), M. utrculata (Osnovka, Cheremkhovo, chetu, and Jargalant Formatons, Lower-Mddle Jurassc), M. magna Sntsh., 1985 (Uda Formaton, Upper Jurassc), M. zolenss Sntsh., 1990 (Bokhto Formaton, upper part of the Lower Jurassc), M. mongolca Sntsh., 1989 (Ulaan Ereg Formaton, the Upper Jurassc), and M. tushlgae Sntsh., 1989 (Hamar-Huburn Formaton, the Lower Mddle Jurassc). M ate r a. Besdes the holotype, paratypes PN, nos. 4626/227 (outcrop 9/O), , 248, 250 (outcrop 9/16), 4626/251 (outcrop 9/2), 4626/253, 255, 260, 271 (outcrop 9/1 ), fragments of nymphs. Famly Hexagentdae Lameere, 1917 Genus Sberogentes Sntshenkova, 1985 Sberlogentes rectcostals Slnltshenkova, sp. nov. Plate 11, lg. 4 Et y mo logy. From Latn rectus (straght) and costa (rb). Ho lot y p e. PN, no. 4626/221, part and counterpart of nymph abdomen wth glls; Chemovske Kop Localty, outcrop 9/3; Upper Jurassc. PALEONTOLOGCAL JOURNAL Vol. 34 No. l l J

6 NEW MAYFLES 73 ~ seta /avnths t ts nal hese - tter herc. val o- ng. the ng of es.9, to ~g- ~ta d 9 ' -j. t s e - e, '.. '! r ~) ~ CFJ ~8 ~ (d) Fg. 2. Nymphs of mayfles of the famles Hexagentdae and Sph!onurdae: (a) Sberoge11tes rectcostals sp. nov., holotype PN, no ; tb) Mesobaets amplectus sp. nov., holotype, no. 4626/201; (c) Stackelbergsca clara sp. nov., holotype PN, no. 4626/232; ld) Sphangarus mtu11jus sp. nov. holotype PN, no. 4626/202. Scale bar 2 mm. Des c rp t on (Fg. 2a). Nymph. Abdomnal segments are rectangular. Segments n the mddle part of abdomen are twce as wde as long. The nner rbs on the glls run close to each other at the base and dverge at a sgnfcant angle; the nner rb s straght. Measurements (mm): the length of abdomen s 13, the complete length of the nymph near 18. Comp a r son. Dffers consderably from known speces n the straght nner rb on the glls. Mate r a. Besdes the holotype, paratype PN, no. 4626/212, a fragment of a nymph from the same bed. Famly Sphlonurdae Ulmer, 1920 Genus Mesobnets Brauer, Redtenbacher et Ganglbauer, 1889 Mesobaets amplectus Snltshenkovn, sp. nov. Plate 11. fg. 5 Et y mo o g y. From Latn amplect11s (embracng). Ho o type. PN, no. 4626/201, mpresson of the head and thorax; Chemovske Kop Localty, outcrop 9/1; Upper Jurassc. Des c rp t on (Fg. 2b). Nymph. The head s rounded, 0. 7 tmes the wdth of the pronotum. The pronotum has a deeply concave front margn and a notably concave hnd margn. The pronotum s 2.6 tmes as wde as long. The mesonotum has rounded front angles. Dstnct three-branched RS and smple MA, MP, CuA, and CuP on the fore wng sheath are present. The hnd wng sheaths are rounded. Measurements (mm): the length of the holotype s 5.5, the full length of the nymph approx. 20, and the length of mddle nstar nymph (paratype) (c) C o m par son. n the shape of the pronotum wth the concave front margn the new speces resembles M. sbrca Br., Redt. et Ganglb., 1889, but dffers n the rounded angles of the mesonotum and large sze. Mater a. Besdes the holotype, paratype PN, no. 4626/240, a complete poorly preserved nymph (outcrop 9/16). Genus Stackelbergsca Tshernova, 1967 Stackelbergsca clara Slnltshenkova, sp. nov. Plate. fg. 6 Et y mo o g y. From Latn clarus (clear). Ho o type. PN, no. 4626/232, part and counterpart of nearly complete nymph wth glls; Chernovske Kop Localty, outcrop 9/3; Upper Jurassc. Des c rp t on (Fg. 2c). Nymph. The head s rounded wth a smoothly convex hnd margn, a lttle narrower and nearly 3 tmes as long as the pronotum. The pronotum s short, 4 tmes as wde as long, wth nearly straght sdes. The abdomen s almost 4.5 tmes as long as the thorax. The abdomnal segments have an undulate front margn. The md part of the eghth segment s slghtly convex, that of the sxth and seventh s strongly convex, wdely rounded at the tp, the tp of the mddle outgrowth of the fourth and ffth segments s nearly acute. Segments of the mddle part of the abdomen are nearly twce as wde as long. The glls are oval-shaped, wth the md-rb placed nearer to the outer margn. Measurements (mm): the length of the holotype s 10.4, the body length approx. 10. C o m p a r s on. n sze and gll structure the new speces s close to S. shaburenss Sntsh., 1991, from whch t dffers consderably n the undulate bases of the abdomnal segments. PALEONTOLOGCAL JOURNAL Vol. 34 No. 2000

7 !! Mater a. Besdes the holotype, paratypes PN, hos. 4626/206, 209 (outcrop 9/1), 4626/214, 231, 232, ~74, 275 (outcrop 9.3), (outcrop 9/10), ~part and counterpart), 4626/236 (outcrop 9116), nymphs. Genus Sphangarus Sntshenkova, gen. nov. Et y m o o g y. From the genus Sphlonurus and ~ngara-land. 1 Type speces. S. rotundus sp. nov. \ D a g nos s. Nymph. Large mayfles wth large lateral eyes and short legs. Sdes of abdomnal segn\lents convex and rounded, angles of segments r~unded. Glls lamellate, oval-shaped. Composton. Monobasc. : C o mp a r s o n. Dffers sharply from other genera ~ the rounded sdes of the abdomnal segments. Spharrgarus rotundus Soltsbenkova, sp. nov. Plate 11, fg. 7 1 Et y mo o g y. From Latn rotundus (rounded). \ Ho lot y p e. PN, no. 4626/202, nearly complete an~ well preser\red nymph of the fnal nstar (part and co~nterpart); Chernovske Kop Localty, outcrop 9/1; U~per Jurassc. \Des c rp t on (Fg. 2d). Nymph. The head has a convex fore margn. The pronotum s short, not wder than the head. The metathorax s short, hnd wng sh~aths are hdden under the fore wng sheaths. The mddle femora are short and broad, 2.5 tmes as long as wde. The tbae 0.6 tmes as wde and 1.37 tmes as long as the femora. The tarsus s 0.56 tmes the length an4 halt the wdth of the tba, the claw s long 0.8 tmes the[length of the tarsus. Abdomnal segments are short, the!fourth segment, whch s wdest, s 2.83 tmes as wqe as long. The nnth abdomnal segment has no nd~ntatons latero-posterorly. ~ea sure men ts (mm): the length of the holotyptf 20.6.,,ate r a. Besdes the holotype, paratypes PN, nos., 4626/205, 254, 266 (outcrop 911 ), 4626/211, 213, 215~ 272 (outcrop 9/3), 4626/216, 223 (outcrop 912), 462?1233, 242 (outcrop 9116), fragments of nymphs. REFERENCES Jell, \P.A and Duncan, P.M., nvertebrates, Manly nsects, from: the Freshwater, Lower Cretaceous, Koonwarra Fossl SNTSHENKOV A Bed (Korumburra Group), South Gppsland, Vctora, n Plants and nvertebrates from the Lower Cretaceous Koon- ' warra Fossl Beds, South Gppsland, Vctora, Jell, P.A. and Roberts, J., f!ds., Sydney: Ass. Australas. Paleontols., 1986, pp Kluge, N.Yu., New Data on Mayfles (Ephemeroptera) from Mesozoc and Cenozoc Resns, Paleontol. J., 1993, vol. 27 (A), pp Martll, D.M., Fossls of the Santana and Crato Formatons, j Brazl, n Palaeontol. Assoc. Feld Gudes to Fossls, Lon-. don, 1993, no. 5. McCafferty, W.P., Chapter 2. Ephemeroptera. nsects from the Santana Formaton, Lower Cretaceous, of Brazl, Bull. Amer. Mus. Nat. Hst., 1990, no. 195, pp Sntshenkova, N.D., New Early Cretaceous Mayfles (lnsecta, Ephemeroptera) from Eastern Transbakala, Paleontol. Zh., 1976,no.2,pp Sntshenkova, N.D., Mesozoc Mayfles, wth Specal Reference on Paleoecology, N ntern. Conf on Ephemeroptera, Bechyne 4-10 Sept nst. Entomol. Czech. Acad. Sc. Cesky Budejovcem,Abstracts, pp Sntshenkova, N.D., Jurassc Mayfles (Ephemerda = Ephemeroptera) of Southern Sbera and Western Mongola; n Tr. Paleont. nst., Akad. Nauk SSSR (Moscow), 1985, vol. 2ll, pp Sntshenkova, N.D., The Mayfles (Ephemerda = Ephemeroptera), n Tr. Sovm. Sov.-Mong. Paleont. Eksped. (Moscow), 1986, vol. 28, (nsects n the Early Cretaceous ecosystems of Western Mongola), pp Sntshenkova; N.D., New Mesozoc Mayfles (Ephemerda) from Mongola, Paleontol. Zh., 1989, no. 3, pp Sntshenkova, N.D., The Mayfles. Ephemerda, n Tr. Paleont. nst., Ak.ad. Nauk SSSR (Moscow), l 990a, vol. 239, (The Late Mesozoc nsects of Eastern Transbakala), pp Sntshenkova, N.D., Mayfles n the contnental Cretaceous deposts, n Kontnental'ny met SSSR (Contnental Cretaceous of the USSR), Vladvostok: Akad. Nauk SSSR, Far East Branch, 1990b, pp Sntshenkova, N.D., New Mesozoc Mayfles from Transbakala and Mongola, Paleontol. Zh., 1991, no. l, pp Sntshenkova, N.D., New Upper Mesozoc Stonefles from Central Transbakala (lnsecta: Perlda = Plecoptera), Paleontol. Zh., 1998, no. 2, pp Sntshenkova, N.D. and Zherkhn, V.V., Mesozoc Lacustrne Bota: Extncton and Persstence of Communtes, Paleontol. J, 1996, v. 30, No. 6, pp Zherkhn, V.V. and Kalugna, N.S., Landscapes and Communtes. Jurassc Contnental Bocenoses of South Sbera and Alled Areas, n Tr. Paleont. nst., Akad. Nauk SSSR (Moscow), 1985, vol. 213, pp \.. l PALEONTOLOGCAL JOURNAL Vol. 34 No. l 2000