A NEW CORYPHODONT FROM THE EOCENE OF SINYU,KIANGSI

The occurrence of the fossils of the coryphodont pantodont at Ninchiashan locality in Sinyu District,Kiangsi has been mentioned in several occasions (Chow,1959;Chow and Tung,1962;Chang and Tung,1963),but none of the specimens found are well pre- served enough for a precise determination.Recently a good mandible with perfectly pre- served P_2—M_3 collected by a field party of Peking Natural History Museum;and,on this bases,a description of all the coryphodont specimens,belonging evidently to one species, from this locality is made in the present paper. Coryphodon ninchiashanensis sp.nov. Type:A mandible with right P_2—M_3 and left P_2—M_2 in the collection of PNHM (PMMA.214).Other material:a complete left lower jaw (paratype);posterior part of another lower jaw and fragmentary limb bones(IVPP.V.3047). Locality and Horizon:Ninchiashan,Sinyu,Kiangsi;middle member of Sinyu formation,Lower Eocene. Diagnosis:A large-sized species of Coryphodon.Lower incisors relatively small;lower canine large and long,with upper part turns backward and slightly outward, and elliptical in cross section,antero-posteriorly elongated;lower premolars with wide open V crest,forming an angle of greater than 60°,crista obliqua lingually placed,paraconid well developed;trigonid of lower molars large,V-shaped crest with strong anterior limb,and internal end of crista obliqua close to metaconid;on M_2 metalophid and hypo- lophid inclined in stead of normal to the longest axis of the tooth.Lower jaw robust, vertical ramus with anterior border nearly perpendicular to the alveolar border of the horizontal ramus. Description and comparison:The single incisor (Ⅰ_1) known is triangular in cross section at the base of crown,with convex labial side and weak cingulum.A short diatesma,as long as the length of P_2,is present between C and P_1.P_1,known only from the paratype,with long trigonid consisting of V-shaped crests forming an angle of about 135°.This angle becomes smaller in the following teeth.Paraconids of Pre- molars become progressively weaker and metaconid strogger from P_1 to P_4.P_2 elongate,with small anterior end,blunt wider posterior side,and paraconid more prominent than metaconid.P_3 compressed antero-posteriorly,with wider tylonid and cingula at anterior and postero-external sides.P_4 larger than P and with metaconid stronger than paraconid. Lower molars elongate,with tylonid sightly lower and narrower than trigonid.M_1 with two limbs of V crests equally developed and form an angle of about 60°;oblique crest rather strong;cingulum weak and discontinuous.M_2 larger than M_1 and with weaker anterior crest of trigonid,M_3 with anterior crest of trigonid M_3 with anterior crest of trigonid still weaker,angle between trigonid V's smaller,posterior cingulum stronger. In addition to the teeth and lower jaws,referable to the same form are some limb bones,including a scapula and proximal part of a humerus etc.The scapula has smaller acromion in comparison with those in C.testis and C.radians.The humerus has broad and shallow bicipital groove and the greater tuberosity higher than the head. The new form resembles closely the genus Coryphodon in the structure of mandible and teeth (see ratio diagram in Fig.2).It is similar to C.armatus in having slanting parallel metalophid and hypolophid.It seems to show more resemblance than other known species of the genus Coryphodon to the Asiatic genus Eudinoceras in having ver- tical ramus with nearly vertical anterior border and some other details.