30 Worlman — Studies of Eocene Mammalia in the 



Omomys Carteri Leidy. 



Omomys Carteri Leidy, Proc. Acad. Nat. Sci. Phila., April, 1869, and 

 Extinct Fauna of Dakota and Nebraska, 1869, p. 408, pi. xxix, figs. 13, 14 ; 

 Hemiacodon nanus Marsh, this Journal, August 13, 1872, p. 213 ; Palaeaco- 

 don vagus Marsh, this Journal, September, 1872, p. 224. 



The type of this genus and species consists of a right man- 

 dibular ramus containing the third and fourth premolars 

 and the first and second molars, together with the alveoli of all 

 the remaining teeth of one side of the jaw. The specimen was 

 found by the late Dr. J. Yan A. Carter, near Grizzly Buttes, 

 in the Bridger Basin, and is preserved in the collection of the 

 Philadelphia Academy. A comparison of the type of Hemiac- 

 odon nanus with Leidy's very excellent figure, as well as with 

 Osborn's outline drawing from a photograph of the type of 

 Omomys Carteri, renders it perfectly clear that the two are 

 not only generically but specifically identical. Another type 

 which in all probability belongs to this species is Palceacodon 

 vagiis. This latter consists of three superior molars of the 

 right side in perfect condition. In no specimen of the fifty or 

 more individuals of Omomys Carteri contained in the Marsh 

 collection are there upper and lower teeth in association, and I 

 base my opinion that these superior molars of Palceacodon 

 vagus are the upper teeth of 0. Cartei'i upon the following 

 considerations : In a closely allied species of the same genus, 

 0. pucillus, in my own collection, there are upper and lower 

 teeth which were found together in such a way as to render it 

 reasonably certain that they belong to the same individual ; 

 there is a decided resemblance between the structure of the 

 corresponding teeth of the two forms ; in size the teeth of P. 

 vagus correspond almost exactly with what the upper teeth of 

 0. Carteri should be, as indicated by the relative measure- 

 ments of the upper and lower teeth of Hemiacodon gracilis, 

 Tarsius spectrum, and Anaptomorj>hus homuncidus, in all of 

 which the upper teeth are known ; they do not agree in size 

 with the lower teeth of any other known species of Bridger 

 Primate. I therefore conclude that the type of Palceacodon 

 vagus refers to the upper teeth of Omomys Carteri. 



Description of the Type of Hemiacodon nanus. 



The specimen upon which Professor Marsh established this 

 species consists of a fragment of a right mandibular ramus, 

 figure 120, containing the fourth premolar and all three molars 

 in perfect preservation. The crown of the fourth premolar 

 when seen from above has a somewhat squarish outline, slightly 

 wider behind than in front, and is composed of a main central 

 pointed cusp which arises a little above the level of the cusps of 

 the molars. Upon the outside this cusp is convex, and internally 



