CENOZOIC CHELONIAN FOSSILS FROM NANHSIUNG,KWANGTUNG

Apart from a very large form of Cretaceous turtle from Nanhsiung,Kwangtungwhich has been described by the present writer(Yeh,1966),there are still manyCenozoic turtles of the same county.The specimens were collected respectively by twoparties of the Institute of Vertebrate Palaeontology and Palaeoanthropology in two sea-sons of 1962—1963 and 1963—1964 from Lofochai Formation chiefly of Nanhsiung Cityregion and Hokou,north-eastern of Nanhsiung.The materials of former locality arebroken,while those of latter one are somewhat better and can be recognized as twonew forms referable respectively to Dermatemydidae and Emydidae which are descri-bed as present note.Family DermatemydidaeGenus MongolemysMongolemys australis,sp.nov.(Text-fig.1;Pls.Ⅰ—Ⅳ)Type A posterior part of about two-thirds carapace and plastron.Field No.63084. 6;Cat.No.of IVPP V 3107.Other Materials A slightly compressed carapace and plastron with its structureof carapace mostly damaged;a compressed carapace and plastron;a carapace andplastron with its postero-lateral part of right broken;a posterior part of plastron;aposterior part of carapace and plastron;a posterior half of carapace and plastron;anearly complete plastron;and other fragments.Field No.63084. 6;Cat.No.of IVPPin due order V 3107.1—3107.8. Locality and Horizon Chihshapai,Hokou,Nanhsiung,Kwangtung.Lower partof Lofochai Formation,Paleocene.Diagnosis Medium size,shell slightly arched,no distinct ornamentation on sur-face of shell.Nuchal plate wide,eight neurals,first ovoil,others hexagonal withshort-lateral border in front.Eight pairs of costal plates which separated entirely byneurals.Costal scutes wide,costo-peripheral suture well above costo-marginal sulcus,free border of peripherals thin.Plastron large and broad,not reduced in size,con-nected suturely with carapace.Bridge broad,length from axillary to inguinal notchlonger than that of anterior or posterior lobe of plastron.Four inframarginals,gularpresent,but no intergular.Entoplastron intersected by humero-pectoral,middle part offemoro-anal extented forwards.For measurements and other structural characters of the new species the reader is referred to the accompanying table and figures in the Chinese text.Remarks The characters of Family Dermatemydidae is very various,most mem-bers of it are lack of hinder neurals,the posterior one or two pairs of costals thusmeet their follows in middle line.The plastral lobes of it are in nearly all casesshortened and narrowed,and the scutes of anterior lobe usually vary in numbers,somefurnished with intergular,gular,humeral,and pectoral,others have only three or eventwo scutes.However,in other hand,there are still some members bearing a full seriesof neurals and with a well developed plastron.They are regarded as primitive formsof the Family.The specimens from Nanhsiung furnished with a full set of neurals and with a welldeveloped plastron are indeed a form of least modified of the group.It is thereforevery near to the genera Mongolemys and Zangerlia of Upper Cretaceous of MongolianPeople's Republic.Because the Zangerlia is a large land tortoise and with pock-markedsculptures on its all shell plates,it seems better to consider our specimens as a memberof Mongolemys which is small.The genus Mongolemys was established by Khosatzkyand Mlynarski in 1971,and represented so far only by its genotype—M.elegans. Inview of the detailed structure between M.elegans and Nanhsiung specimens,the Mon-golian form differs still from ours in following points:1)weaked epiplastron,2)elongated entoplastron,3)humero-pectoral sulcus behind the entoplastron,4)narrowedposterior lobe of plastron,5)plastron truncated anteriorly,and 6)fine sculpture onthe plates.By the reasons just mentioned,the present writer considers the materialsfrom South China as a new species of the Mongolemys named as Mongolemys australissp.nov.The materials of Dermatemydidae so far known in China are very rare,althoughfive genera having been described from Mesozoic,of which two are still doubtfull insystematization.Of the Cenozoic,there was only one species of Adocus of Eocenerecorded by Gilmore from Inner Mongolia.All these specimens were collected fromNorth China.The present form therefore represents the first occurrence of Dermate-mydidae found in South China.Family EmydidaeGenus Hokouchelys gen.nov.With the diagnosis of the type species Hokouchelys chenshuensis.Hokouchelys chenshuensis sp.nov.(Text-fig.2;Pls.Ⅳ—Ⅴ)Type An emydid carapace consists of the nuchal,1—3 neurals,and 1—3 costalsof left.Field No.6227;Cat.No.of IVPP V 3108.Other Materials A piece of carapace including 2—3 neurals and parts of cos-tals;a well preserved axillary buttress of right and parts of carapace and plastronarticulated with it;a right inguinal buttress and 5—6 costals;three connective peri-pherals of bridge;a complete plastron;and other fragments.Field No.6227;Cat.No.of IVPP in due order V3108.1—3108.6. An anterior half of plastron and other fragments.Field No.6228;Cat.No.of IVPP V3109.Locality and Horizon V 3108—3108.6:about one Km.west of Hokou,Nan-hsiung,Kwangtung;V3109:about two Km.north-west of Hokou.Upper part ofLofochai Formation,Paleocene or Early Eocene.Diagnosis Shell long,first neural ovoid,second,third,sixth,and seventh(? )hexagonal,and with their short-lateral borders in front.First vertebral pentagonal,wider anteriorly.Plastron broadly sutured with carapace,length of bridge longerthan that of anterior or posterior lobe of plastron.Axillary and inguinal buttressesextremely developed,articulating respectively with inner surfaces of first,fifth andsixth costals.Anterior border of plastron notched shallowly,posterior one of it not-ched widely.Humero-pectoral behind entoplastron.Other structural characters of the new species are referred to the figures in theChinese text.Remarks One of the important characters of present specimens described aboveis the extremely developed axillary and inguinal buttresses.According to the records,there are five genera of Emydidae in Asia also with such a structure.They aregenera Kachuga,Hardella,Batagur,Callagur,and Ocadia.Among these generaBatagur and Callagur are only recorded by living species;Kachuga and Hardellathough having few representatives of Pliocene,they are chiefly of living forms.Stratigraphically,the genus Ocadia,which distributed from Eocene to recent,is thenearest of new form,but it differs from ours in two points:the entoplastron of it iscrossed by humero-pectoral,the buttresses of it are less developed.The genus Echmatemys of Eocene of North America is also characterized by thedeveloped buttresses.It distinguishes from Asiatic genera mentioned above chiefly inabsence of the developed longitudinal ridge in the triturating surface.Because thereis no skull found together with our specimens,it is not available to determine whetherthe new form is near to American or Asian.In view of the structure of the shell,wecan still separated present form from American by the absence of epiplastral lip,andby the relative position of entoplastron and humero-pectoral.With the exception of Gyremys,a doubtful emydid of Upper Cretaceous,so faras the present knowledge known,the earliest representative of Emydidae is the genusClemmys of Paleocene.The axillary and inguinal buttresses of this genus are feeble,it is a character quite different from new genus Hokouchelys of Paleocene proposedhere.The fact seems to indicate that there are at least two different evolutional lineseven in early evolutional stage of Emydidae.Besides the specimens just described above,there are still some other fragmentselse of fossil turtles collected also from Lofochai Formation.They are too bad formaking an exact determination.