722 



KANSAS CITY REVIEW OF SCIENCE. 



These he calls Condylarthra and Diplarthra. Their distinctive characters are 

 found in the inferior extremity of the astragalus, — and its manner of articulation 

 with the cuboid and navicular bones. In the former the distal face of the astra- 

 galus is convex in every direction, and articulates with the navicular alone, while 

 in the latter this portion of the bone is considerably flattened and unites with both 

 navicular and cuboid, although the surface for the latter is quite small and insig- 

 nificant in comparison with the former. The Condylarthra includes as yet 



Fig. 2. Fig. 3. 



Right posterior foot of P>-(7/<)Az>5/«fj</'««£r/«j Cope, Right posterior foot of Poebrotheriunt labiaium 

 from Colorado, about one- half natural size. From Cope from Colorado, three-fifths natural size. From 

 Report U. S. Geol. Sur. Terrs. F. V. Hayden, iv. Hayden's Report, iv. Pi. cxv. 



two families, Phenacodontidcs and Menisco theriidcB, whose remains have been 

 found so far only in the lower Eocene deposits of this country. It is interest- 

 ing to note that they are the most generalized of any known Perissodadyla, and 

 supply us with a link long and earnestly sought for in the evolution of the 

 latter and more specialized forms of this order. The feet are considerably 

 shortened and furnished with five toes in functional use upon each, a character 

 which at once constitutes an approach to the Amblypoda. The molar teeth are 



