1(50 
TiENTODONTA. 
on the convex face of the tooth, and not far from tlie grinding-face tliey 
unite, surrounding that side of the end of the crown. Tlie enamel bands 
are also slightly incurved on the concave face, increasingly so near to the 
grinding-face, but they do not meet by a considerable interval. The 
masticating surface is therefore oblique, wearing faster on the side not 
protected by the enamel. On the opposite side, the enamel is thrown into 
an entering fold of little depth at the point to which the crown is worn in 
the specimen, which runs out a little above the grinding-face. There are 
some obsolete strise on the enamel toward the decurved margin. The 
pulp-cavity is large at the fractured base of the tooth, and is surrounded 
by thick dentinal walls. 
Measurements. 
M. 
Length of the crown preserved.... 0.038 
iJepth of the crown at the broken base... 0. 018 
Depth of the crown at the apex....... 0. 011 
Width of the crown at the broken base... 0. 008 
Width of the crown at the apex. , . 0. 006 
Width of the interruption in the enamel at the grinding-face.... 0. 005 
In comparison with the corresponding tooth of the JE. gliriformis^ the 
following peculiarities may be observed: the convergence of the enameled 
faces is much less rapid in E. novomehicanus; the flat side of the former is 
replaced by a concave side in the latter; the convex side of the E. novonie- 
Jiicanus, is in E. gliriformis grooved next the lower or posterior side, the 
enamel band standing out in a bead; this groove becomes deeper, and 
finally divides the apex into two; in E. novomehicanus., this groove is only 
apparent near the apex, and the enamel bands are continuous with the 
intervening surface except at that point; the anterior enamel band is more 
strongly incurved on the flat side near the apex in the E. gliriformis. 
Ectoganus gliriformis, Cope. 
Plato xli, figs. 1-12. 
Report Vert. Foss. Xew Mexico, C. S. Geog. Snrvs. W. of 100th M., 1874, p. 5; Id., 
Ann. Report TJ. S. Geog. Snrvs. W. of lOOtb M., 1874, p. 110. 
The teeth constitute the available representatives of this species; the 
cranial and other fragments found being useless for description. 
The superior enamel face of the superior incisor has an open shallow 
groove near the supero-anterior margin. The face of the superior apex, 
