166 
T^NIODONTA. 
An incisor of another individual displays the same characters; i. e., the 
posterior truncation below the apex, the equal antero-posterior diameter, 
and the broadly convex ungrooved front. The size is a little smaller. A 
portion of a third individual is similar. 
Calamodon simplex, Cope. 
Plates xlii, tigs. 6-8 ; xliii; xliv, figs. 2-5. 
Eeport Vert. Foss. New Mexico, U. S. Geog. Survs. W. of 100th M., 1874, p. 5; Id., Ann. 
Eeport U. S, Geog. Survs. W. of 100th M., 1874, p. 117. 
The remains of this species were found rather more abundantly than 
those of the C. arcamoemis, from which it differs but little in dimensions. It 
may be distinguished by the form of its inferior incisor teeth, which are 
more robust and more roughened by longitudinal striae or grooves. The 
most marked of these is a shallow concavity near the external posterior bor¬ 
der, which destroys the regular convexity seen in the C. arcamcenus. The 
median portion of the face is more protuberant and the investiture of enamel 
extends more posteriorly on both sides, the external border lying along 
the summit of a low longitudinal rib of the dentine. The posterior border of 
the shaft contracts gradually to the trenchant apex in front, as in JEctoganus 
gliriformis, and is not truncate, as in 0. arcamcenus. 
The specimen of this species first described consists of portions of 
inferior incisors and a molar. The former are larger than those of the G. 
arcamcenus, and the enamel face is protuberant, having a greater posterior 
extent than in that species; one side is gently convex, and is marked with 
a number of obsolete longitudinal ribs; the oj)posite face is turned outward 
at its posterior border, forming an open concavity. This side also is marked 
by obscure longitudinal ribs. The enamel surface is obsoletely rugose, 
except near the apex, where it is smooth. The molar is elongate, simple, 
and gently curved. Its section is obtusely subquadrate, and the external 
face, which is convex longitudinally, is also more convex in cross-section 
than the other sides. The external face has an investiture of enamel to 
near the base, while the dentinal surface extends to near the triturating sur¬ 
face on the anterior and posterior faces. The enamel of the inner face 
descends to a pointed extremity which marks half the length of the external 
