444 Prof. EF. D. Cope—On the Proboscidea. 
I. Intermediate molars with not more than three crests (trilophodont). — 
a. Crests acute, transverse. 
8. Valleys uninterrupted. 
Last superior molar with three crests and a heel; crests low, not serrated.—T. 
brevidens. 
Last superior molar with four crests and a heel; crests elevated, not serrated.— 
IM. Americanus. 
BB. Valleys interrupted. 
Edge of crest tuberculate.— 7. serridens. 
aa. Crests transverse, composed of conic lobes. 
B. Valleys little interrupted. 
Last inferior molar narrow, with four crests ; an accessory tubercle in each valley. 
D. shepard. 
B. Valleys interrupted. 
Last inferior molar with four crests and a heel ; symphysis short, M. 150; smaller 
size.— 7. euhypodon. : 
Last inferior molar with four crests and a cingulum, symphysis longer, M. 280. 
Size medium.— 7. productus. : 
Last inferior molar with five crests and a heel, symphysis very long, M. 450. 
Size largest.—T. angustidens. 
‘aaa. Crests broken into conic lobes ; those of opposite sides alternating. 
Last inferior molar narrow, supporting four crests and a heel.—T7. obscwrus.’ 
II. Intermediate molars with four transverse crests (tetralophodont). 
A long symphysis ; crests well separated, tubercular, with accessory lobes inter- 
rupting valleys.—T7. campester. 
Symphysis very short; crests thick, closing valleys by contact; no accessory cusps 
(Leidy).—W. mirificus. 
III. Intermediate molars with 9-16 crests. 
B. Valleys filled with cementum. 
Last molar with 18-27 cross-crests.— Elephas primigenius. 
The stratigraphical position of these species is as follows :— 
Pleistocene. 
Mastodon americanus, 
Elephas primigenius (less abundant). 
Pliocene. 
Elephas primigenius (more abundant.) 
Tetrabelodon serridens (horizon probable). 
Dibelodon shepardi 
Upper Miocene (Loup Fork). 
Tetrabelodon euhypodon. 
55 productus. 
3 angustidens. 
50 campester. 
Mastodon mirificus. 
Ticholeptus bed. 
Tetrabelodon brevidens.”’ 
Prof. Cope then proceeds to give an account of the American 
species, M. (Tetrabelodon) obscurus, Leidy, M. (Dibelodon) Shepardi, 
Leidy; the latter of which is from the Pliocene of the valley of 
Mexico. M. (Tetrabelodon) brevidens, Cope, is the oldest North 
American species, and presents a very simple type of molar: it is 
from the Ticholeptus bed of Montana. M. Tetrabelodon angustidens, 
Cuv., occurs in the Loup Fork beds of Kansas, Nebraska, and 
Dakota. The molar teeth exceed in size those of the typical 
European form. “It may become necessary,” says Prof. Cope, ‘to 
distinguish this form as a species under the name of Teérabelodon 
proavus.” ‘The author adds that, ‘ Probably this species has been 
