28 Bulletin American Museum of Natural History. [Vol. XIV, 



Type of the genus Prototomus. Wasatch assise, New Mexico 

 and Wyoming. The small size distinguishes it from any other 

 Wasatch species. Judging from Professor Cope's figures it is 

 also distinguished by the simplicity of p-, which is little more 

 molariform than p^ of the larger species. The species appears 

 to be quite primitive in other characters as well, and I am dis- 

 posed to place with it a few lower jaw fragments in our collec- 

 tions containing molars of appropriate size in which, while the 

 trigonid is high, the metaconid is better developed, the shear 

 more transverse, and the whole tooth wider than is usual in the 

 genus. {Am. Mus. Nos. 94 and ?297i.) 



Sinopa opisthotoma, sp. nov. 



Siypolophus sp. innom. Osborn & WoRTMAN, Bull. Am. Mus. Nat. Hist. 

 i8g2, no. " No. 99 is much larger than any described species of Siypolophus." 



Wasatch assise, Wyoming. 



Fig 9. Sinopa opisthotoma Matthew. Upper and lower jaws, three- 

 fourths natural size, type specimen No. gg, Wasatch Beds, Big Horn Basin, 

 Wyoming. Amer. Mus. Exp. i8gi. W, upper jaw, from below; B, lower 

 jaw, from outside ; C, from above. 



With the type (No. 99), upper and lower jaws, teeth well pre- 

 served, I associate provisionally No. loi, upper and lower jaw 



