Marsh Collection, Peabody Museum. 435 



cusps, more or less fused or well-separated external cusps, and 

 with anterior and posterior external angles produced into shear- 

 ing blades ; with first premolar above, and first and frequently 

 second below, spaced ; with first lower molar more or less reduced, 

 and becoming progressively smaller and weaker than the others ; 

 and with pentadactyle limbs, in which the ungual phalanges are 

 compressed, curved, and sharp-pointed. 



Sin op a rap ax Leidy. 



Sinopa rapax Leidy, Proc. Acad. Nat. Sci. Phila., 1871, p. 115 ; 

 Stypolophus pungens Cope, Proc. Anaer. Philos. Soc, 1872, p. 446. 



The type species of this genus was described from a lower 

 jaw fragment, carrying the fourth premolar and first molar in 

 good condition, together with the heel of the second and the 

 roots of the third. The specimen, although fragmentary, was 

 well described and figured by Leidy, and it is possible to refer 

 other material to it from the same horizon. Cope in speaking 

 of his genus Stypolophus says : * " Dr. Leidy has applied the 

 name Sinopa to some flesh-eaters of the Bridger epoch without 

 distinctive generic description. An examination of the typical 

 specimen of the S. vorax [rapax], which Dr. Leidy kindly 



83 



Figure 83. — Lower jaw of Sinopa rapax Leidy ; side view ; natural size. 



permitted me, shows that it differs from Stypolophus in the 

 rudimental character of the heel of the last molar, if the speci- 

 men is not deceptive. It is otherwise identical in the last four 

 inferior molars." Now Leidy's specimen is deficient in the 

 matter of the last molar, and it is not possible, according to 

 his figure, to make out anything concerning the crown more 

 than what is stated in the description, which is as follows : f 

 " The last molar is a two-fanged tooth like those in advance, 

 but is not quite so wide, and a small portion of the back of the 

 crown indicates it to have been of less thickness." 



There are two specimens in the Marsh collection, consisting 

 of considerable portions of the mandibular rami. One is a 



* Tertiary Vertebrata, 1884, p. 289. 



f Extinct Vertebrate Fauna of the Territories, 1873, p. 116. 



