1884. ] The Condylarthra. 893 
its inferior true molars come nearer to developing Vs than any 
other genus of the family. The definitions are as follows: 
Last superior premolars with but one external cusp; inferior molars with Vs. 
Protogonia. 
Last superior premolars with two external cusps; inferior molars with well-devel- 
o usps Phenacodus. 
Inferior molars with flat grinding faces; no cusps Anacodon 
Second, third and fourth superior premolars with two external’ cusps; those of infe- 
rior molars well devel ] Diacodexts 
È Zz 
Of these genera the only one which is restricted to the Puerco 
epoch is Protogonia. Some species of Phenacodus are Puerco, 
but the majority are Wasatch, while the two remaining genera 
are Wasatch. 
The two species of Protogonia are known in the Puerco fauna 
as the only ones, with three species of Phenacodus, which possess 
regularly quadrituberculate superior molars. The simplicity of 
their fourth premolar and the absence of the external cingular cusp 
of the superior true molars proclaim them the most primitive 
Species, as they are the oldest, of the family. The smaller spe- 
cies, P. plicifera Cope’ (Fig. 14), has a skull as large as that of a 
terrier dog. The P. subguadrata is 
larger and otherwise different. 
In the genus Phenacodus Cope, we 
have the best known representative of : q 
the order Condylarthra, and the one 
to which the largest number of spe- 
cies is referred. Almost perfect speci- 
mens of the P. primevus (the type) 
and the P. vortmani, were found in the 
Wasatch Eocene sandstone of the Big Fic. 14.—Protogonia plicifera ; 
Tom tiver of Wyoming: (see Plates pis 0h riaa. From the Pues 
XXIX and xxx), beds of New Mexico. Original, 
The dentition includes the normal fopa Labs sa cated 
number found in the least modifed- ° ` 
Mammalia, viz., 1.3; C. ł}; Pm. 4; M.3; and the series is not ín- 
terrupted by important spaces. The canines are weak, and none 
of the premolars in either jaw resemble the true molars. è The 
latter are quadritubercular, with intermediate tubercles both 
above and below. The last inferior molar has a fifth lobe. 
ao 
* The best specimens of this species are not yet figured. 
