352 The Crecdonta. 
Centetidz, and other recent families both of Creodonta and In- 
sectivora (Fig. 23). Of the genera with large canines, Chriacus has 
already been mentioned as having a simple fourth premolar 
with only an internal cusp to distinguish it from the genera 
of Sect. 1 of the family. Its true lower molars have an anterior 
V of three connected cusps. This is also the character of 
the inferior molars and fourth premolar of Deltatherium (Fig 
20), which is also peculiar in having but 3 premolars, and @ 
diastema. In the three genera which remain, the anterior ot 
Fic. 20.—Deltatherium fundaminis Cope, skull and Tamus p "o fA 
natural „size, from the Puerco beds of New Mexico. a mi f i 
; Fig. d from a second animal. Fig. < , Tight side 0 ie side. 
below ; c, mandible, part, nde above; 4, left ramus, ow 
U. S. Geol. Survey Terrs., Vol. 11. Origin nal. 
fifth cusp of the true molars is rudimental. They ©” 
each other in the structure of the third spe f 
In Ictops Leidy, this tooth has two external and i 
cusps; in Mesodectes Cope, there are one cusp 
nal cusps, and Leptictis Leidy, there is no ermal 
external one is simple. 
There are certainly three, and proba ably foun, a 
