Cope.] 84. [Feb. 17, 
shows that the inferior molar structure of the two types mentioned has 
been produced by modifications of a W-shaped type of crown. I note in 
passing, that the type of Pantolambda is itself readily derived from the 
. .... d-tubercular noe. : 
primitive -— iperculat type of primitive placentals and marsupials. 
With these propositions established, I proceed to consider first the origin 
of the dental peculiarities of the CoRYPHODONTID A. 
First, no posterior inner tubercle was developed on the superior molars. 
We may regard this as a consequence of the fact that a transverse (ectal) 
movement of the lower jaw was established before the appearance of this 
cusp, instead of after it, as was the case in other ungulate orders, and 
because the shearing has been always from before backwards, instead of 
Fic. 8.—Superior molar series of Coryphodontids, two-thirds nat. size, from the Wa- 
satch beds of Wyoming. Original. Fig. a, Ectacodon cinctus Cope. Fig. b, Metalopho- 
don testis Cope. 
overlapping from behind forwards, as in all other Ungulata. The stimulus 
already assigned as the cause of the development of the fourth tubercle 
is, under these circumstances, wanting. (Tig. 3.) 
Second, the anterior cingulum, which extends from the internal cusp to 
the anterior external angle of the crown along its anterior base, is greatly 
developed. This may be reasonably ascribed to the stimulus produced 
by the friction of the posterior limb of the anterior V of the inferior molar 
in the transverse movement in mastication. The anterior crest of the 
superior molar is developed instead of the corresponding posterior crest of 
the superior molar in front of it, because the transverse movement of the 
