156 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



of these Eocene lemurs, but as far as we have them 

 (genera Tomitherium and Adapis) they are monkey- 

 like. But we have what is almost as useful, the skel- 

 eton of their Eocene and Puerco ancestors, the Con- 

 dylarthra. I long since pointed out that the latter 

 order (not the genus Phenacodus, as Lydekker has 



Fig- 39- — Tomitherium rostratum Cope, one of the Adapidae, mandible, 

 natural size; a, from left side; h, from above. Original, from Report U. S. 

 Geol. Survey Terrs., Vol. III. 



represented me as saying) must be the ancestors of 

 the lemurs, basing my views expressly on the general 

 structure of the Phenacodus, Periptychus, and Menis- 

 cotherium. The structure of the ungual phalanges of 

 Periptychus is very significant, and even more so is 

 that in Meniscotherium, as recently shown by Marsh, 



