Marsh Collection, Peabody Museum. 435 



other skeletal parts represented. In comparison with the oldest 

 and most primitive undisputed monkeys, a careful examination of 

 these Puerco and Torrejon forms reveals a wide difference in the 

 organization of the two, and it is much to be doubted whether 

 they really have anything in common with the true Primates. 

 It appears necessary, however, to make an exception to this 

 statement in the case of the genus Mixodectes and possibly also of 

 Olbodotes. Matthew believes,* from an associated astragalus, 

 that the former of these. genera belongs to the Eodentia rather 

 than to the Primates, but its successors in both the Wasatch 

 and the Bridger show very strong Primate affinities; hence, 

 there can be little doubt that they constitute an aberrant side 

 branch of the main Primate axis. 



If we thus exclude the Mixodectes- Microsy ops series, the 

 oldest remains of true and undisputed Primates occur in the 

 Wasatch, and there are excellent reasons for the belief that they 

 were new types of sudden introduction in the region, at the 

 beginning of this epoch. Unfortunately, these Wasatch forms 

 are very imperfectly known, so that it is not until we reach 

 the Bridger that anything like complete skeletons have been 

 obtained. Some, at least, of these Bridger types, while true 

 monkeys, were in practically the same state of evolution as 

 many of the existing lemurs, so that by careful comparison of 

 the two groups we are enabled to eliminate the specialized 

 and advanced features and reach the more fundamental primi- 

 tive characters which must have belonged to the ancestors of 

 all Primates. 



There has been relatively little speculation on the definite 

 and more exact origin of any of the great groups of Eutherian 

 mammals, and apparently less on the Primates than any other. 

 Huxley, in his famous paper " On the Application of the Laws 

 of Evolution to the Arrangement of the Mammalia, " expressed 

 the opinion that they arose from a central type of the Insec- 

 tivora, such as the Erinaceidse. Nearly twenty years later we 

 find no less an authority than Hubrechtf warmly supporting the 

 same view. In speaking of Erinaceus and Gymnura, Huxley's 

 exact words are : " in them, even more than other Insectivora, we 

 possess the key to every peculiarity which is met with in the Pri- 

 mates, Carnivora, and the Hngulata. " However much I may be 

 disinclined to dissent from the views of so great a master in mor- 

 phology, we can not disregard the fact that the very large 

 increase in our knowledge of the extinct forms during the past 

 twenty years has materially altered our conceptions of the rela- 

 tions of these groups. It is true that the Insectivora furnish 



*Btill. Amer. Mus. Nat. Hist., 1897, p. 265. 

 f Descent of the Primates, p. 5, 1897. 



Am. Jour. Sci. — Fourth Series, Vol. XV, No. 90.— June, 1903. 

 30 



