AUT. 1. PRIMATES or THE FORT UNION GIDLEY. 9 



tions observed in the last upper premolar, especially, and the differ- 

 ent line of specialization indicated in the anterior teeth of the lower 

 jaw (namely the presence in yaromomys of a well-developed canine, 

 which tooth is entirely wanting in Noihodecies) suggest that the re- 

 lationship of these two groups is not particularly close, although 

 possibly as close as that existing between the Omomids and Noth- 

 arctids. 



Comparing the Paromomys-PalaechtJion species with the Omomys- 

 Hemiacodon species, there is a striking similarity in the general modi- 

 fications of the anterior teeth of the lower jaws, and it is this feature 

 which has suggested the reference of the Paleocene genera to the 

 Tarsiidae, as that family has been defined by Matthew. These two 

 groups possess in common an unreduced canine and an enlarged in- 

 cisor, with reduction or loss of the other incisors — an unusual modifica- 

 tion. Paromomys and Palaechthon, although from the older horizon, 

 had, however, reached a somewhat more advanced stage of develop- 

 ment in respect to the incisors in that the inner one is relatively more 

 enlarged and the lateral ones are either wanting or are reduced to a 

 functionless remnant. Though usually small, the lateral incisor is 

 always quite prominent in Omomys and Hemiacodon. In none of the 

 specimens of the Fort Union species is this tooth clearly indicated, 

 but its presence as a mere vestige is suggested in two of them by 

 what appears to be a segment of a very small alveolar border. Hence 

 this tooth, if present, is vestigial. 



These differences would be considered slight were the geologic time 

 of occurence of the two forms reversed. Since, however, the more 

 advanced stage belongs to the older form, it here becomes important 

 and precludes the possibility of a direct genetic relationship, even if 

 the marked differences in character of the molars were not consid- 

 ered. But the molars also, and especially those of the upper series, 

 indicate, as already intimated, a distinctly different line of develop- 

 ment than is suggested by those of the Omomid group. 



From these comparisons it will be observed that the combined 

 characters, especially of Paromomys, while presenting in the molars 

 certain Notharctid features, indicate a nearer relationship to the 

 Eocene Tarsiids, although they seem to represent a distinctly differ- 

 ent line of development than any of the known later members of the 

 group. The exact place of Paromomys and Palaeclithon in the 

 scheme of classification perhaps can not be assigned with certainty 

 without a much wider knowledge of all of these early Primates than 

 now exists, but I am inclined at present to consider the group rep- 

 resented by these genera as a sixth major division of Matthew's key 

 to the genera of Tarsiidae^ to be defined as follows: 



'Bull. Araer. Miis. Nal. Hist., vol 34, 1915, pp. 447, 448 



