H. F. shorn — Mammalia in North America. 465 



Meniscotherium, a member of the Condylarthra, which it very 

 closely resembles in its skull and molar structure and in its 

 dental curve. Marsh, by the way, has just added to our 

 knowledge of this little Wahsatch genus by describing its fore 

 and hind feet, which are more primitive than those of Phena- 

 codus or Hyrax. While the Creodonta were imitating all 

 modern carnivores, is it not posssible that the Condylarthra 

 gave off a sloth-like form for fossorial and semi-arboreal habits ? 



Last summer while this problem was being discussed, we 

 were brought face to face with the exact counterpart of Chalico- 

 therium which may be called a clawed odd-toed form, by the 

 surprising discovery of a hind foot, which represents &claioed 

 even-toed animal. This was found by the American Museum 

 party in the Protoceras beds of South Dakota, and has been 

 named Artionyx. This foot has a truly Artiodactyl tarsus and 

 metatarsus like that of the pigs or oreodons. Yet it possesses 

 five toes terminating in large uncleft claws. It has been sug- 

 gested by Wortman and myself that it represents an Artiony- 

 chine (even-clawed) division and that Chalicotherium repre- 

 sents a Perissonychine (odd-clawed) division of the Ancylo- 

 poda ; in other words, that a double parallelism exists with the 

 Ungulata. Another explanation may be that these genera are 

 highly specialized Artiodactyla and Perissodactyla respectively ; 

 Scott has made the ingenious suggestion, tending to support 

 this theory, that the Artionyx foot is the long unknown foot 

 of the aberrant oreodont Agriochoerus of Leidy. This sum- 

 mer will probably determine the truth of this suggestion, for 

 two parties are hunting in the beds in which Agriochoerus and 

 Artionyx occur. 



Thus an immense number of problems still await solution, 

 and demand the generous cooperation of European and Amer- 

 ican specialists in the use of similar methods of research, in 

 the prompt publication of descriptions and figures, and in the 

 free use of museum collections. I may be pardoned for calling 

 general attention to the service which the pal^eontological 

 department of the American Museum is trying to render in 

 the immediate publication of stratigraphical and descriptive 

 tables of western horizons and localities. 



Tlte Factors of Evolution. 



A few words in conclusion upon the impressions which a 

 study of the rise of the mammalia gives as to the factors of 

 organic evolution. I refer also to recent papers by Cope, 

 Scott and myself. 



The evolution of a family like the Titanotheres presents 

 an uninterrupted march in one direction. While apparently 



