238 COPE. (Vor. III. 
progress is impossible. It may be objected that the presence 
of the large superior canines forbids any considerable lateral 
movement of the lower jaw. The superior canines are, however, 
so divergent in the Coryphodontidz that such movement is 
possible, and the transversely convex wear of these teeth proves 
just such a movement of the inferior canines on them. The 
lateral movement in the old males of the Dinocerata has been 
much restricted by the superior canines, but in younger males 
and females it was possible. 
A second proposition is demonstrated by the discovery of 
the Pantolambididz. This is, that the superior molars of both 
the Coryphodontide and Uintatheriidz are derived from a type 
with two external V’s (Pantolambda, Fig. 62), and I propose to 
show how this derivation has been accomplished, and under 
what mechanical necessity. Pantolambda also shows that the 
Figure 63.— Superior molar series of Coryphodontidze, two-thirds nat. size; from 
the Wasatch beds of Wyoming; original. Fig. a, Ectacodon cinctus Cope. Fig. 4, 
Metalophodon testis Cope. 
inferior molar structure of the two types mentioned has been 
produced by the modifications of a W-shaped type of crown. I 
note in passing, that the type of Pantolambda is itself readily 
3 — tubercular 
derived from the primitive 2———— type of primitive pla- 
5 — tubercular 
centals and marsupials. 
With these propositions established, I proceed to consider 
