ART. 1. PRIMATES OF THE FORT UNION GIDLEY. 29 



the anterior ends, which extend but shghtly beyond the sacrum 

 attachment, are but Uttle expanded vertically. There is no gluteal 

 fossa and no vestige or suggestion of the anteacetabular process 

 noted by Gregory as being prominent "in Noiharctus and in the 

 lemurs." Moreover, the iha in Perodicticus are strongly attached to 

 two sacral vertebrae and the anterior part of a third, instead of one 

 as noted by Gregory for the Madagascar lemurs. On the whole, the 

 pelvis of Perodicticus much more nearly resembles that of the insecti- 

 vore SoUnodon (see pi. 5, fig. 4), and it is difficult to conceive of its 

 derivation from any such form as that of Notharctus. 



On the anthropoidian side, Gregory seems to have been unfortunate 

 in choosing for his principal comparisons a pelvis of Cehus in which 

 the basic characters are obscured by greatly expanded (modern) 

 ilia. In fact, with all deference to Doctor Gregory's opinion to the 

 contrary, my own investigations, which include a critical comparison 

 of the pelvic structure in all the available forms of lemurs and of 

 South American monkeys, lead me to conclude that after all there is 

 between Notharctus and the South American monkeys a striking 

 similarity in the fundamental structure of the pelvis, and that each 

 modern form is directly derivable, with relatively slight modifications, 

 from the Notharctid type. Comparing the pelvis of Alouatta (see 

 pi. 5, fig. 2), the lyrate form is seen to be quite similar to that ob- 

 served in Notharctus, and would be more strikingly apparent were it 

 not for the slight expansion in Alouatta of the external iliac borders. 

 This lyrate form may be seen also in the pelvis of Cehv^ and Hapale 

 (see pi. 5, fig. 3) and may be traced, although it is much obscured 

 by the still greater expanded ilia, in all anthropoid apes and even in 

 man. Yet Gregory has mentioned this as being one of the main fea- 

 tures in Notharctus which characterize it as being "essentially lemur- 

 ine." Also, the anteacetabular spine, which is conspicuous in Noth- 

 arctus and the Madagascar lemurs, was considered a lemurine char- 

 acter; but this element is entirely wanting in the continental lemurs, 

 while it is still a rather prominent feature in some species of Alouatta, 

 Cehus, and Ilapale. In fact, the transition from the Notharctine 

 type of pelvis to that of any of the Platyrrhini is so slight as to pre- 

 sent no difficulties, especially if obviously modern specializations in 

 the latter are considered. These changes are in each case about what 

 one might expect between an Eocene form and its present day de- 

 scendants. In contrast with this in the modern lemurs, regardless 

 of what group is considered, the pelvis has not advanced in develop- 

 ment beyond, and is still in some respects even more primitive than 

 that of their alleged Eocene ancestors. In view of these facts I can 

 not concede that the Notharctus type of pelvis is "essentially lemur- 

 ine," but believe rather that it stands morphologically between the 

 lemurine and Platyrrhine types with a rather definite trend in devel- 

 opment toward the latter. 



