1884.] The Condylarthra. 897 
The characters of the brain are very primitive, though the 
cerebral hemispheres are better developed than in the Ambly- 
poda, which are themselves superior in cerebral structure to the 
genus Periptychus (Fig. 9). 
S; 18.—Phenacodus primevus ; sacrum and right innominate bone minus much 
Oe Pubis, individual mE ace fo in Plate xxIx; one-half nat. size, from below. 
ginal, from Report U. S. Geol. Survey Terrs., Vol. 111. 
I refer nine species to this genus. Of these only two, P. prim- 
Zvus and P, vortmani are sufficiently well known to render the 
