134 Wortman — Studies of Eocene Mammalia in the 



and there is a distinct ridge descending from the external cusp 

 of the heel into the valley — a structure which is wanting in 

 0. Carteri / the crown of the last upper molar is not so 

 pointed internally; the postero-internal cusp is better devel- 

 oped upon the second than on the first molar ; the interme- 

 diates are a little less distinct than in O. Carteri. 



The species is thus far known from the lower and middle 

 horizons of the Bridger. 



Omomys Ameghini sp. nov. 



A third still smaller species, which I refer provisionally to 

 this genus, is represented by a fragment of a lower jaw of the 

 left side, containing the second and third molars, figure 127. 

 Besides being smaller in size than that of O.pucilhcs, the trigon 

 is elevated above the heel to a much greater extent. This gives 

 a somewhat insectivorous appearance to the teeth, but they are 

 otherwise as in the species of Omomys. 



126 127 



Figure 126. — Crown view of three superior molars of the right side of 

 Omomys puciUus Marsh ; two and one-half times natural size. 



Figure 127. —Jaw fragment of the left side of Omomys Ameghini Wort- 

 man ; side and crown views ; two and one-half times. natural size. (Type.) 



The last molar is little reduced, and the anterior cusp of the 

 trigon is distinct in both the second and third. 



The locality from which the specimen was obtained is not 

 mentioned on the label, unfortunately, so that its exact horizon 

 is unknown. The specimen was found by Mr. J. W. Chew. 



Omomys xdntensis Osborn. 



Microsyops uiyitensis Osborn, Bull. Amer. Mus. Nat. Hist., 1895, p. 77; 

 ibid., June 28, 1902, p. 202. 



This species of Omomys was founded upon a fragment of 

 jaw from the Uinta, containing the third and fourth pre- 

 molars and the first and second molars. The specimen is pre- 

 served in the American Museum collection, and has recently 

 been figured by Osborn in his paper on the American Eocene 

 Primates. At the time of its description, Osborn referred the 

 specimen to the genus Microsyops, but in his last paper that 

 reference is considered erroneous. After a careful examina- 

 tion of the type and a detailed comparison with Omomys, I 

 am- fully convinced that it is the Uinta representative of this 



