482 THE AMERICAN NATURALIST. [VoL. XXXII. 
vidual, being much smaller, thinner, and less worn on the tritu- 
rating surface than Mr. Teller’s specimens. Very remarkable 
indeed is the spiniform projection at the symphysis, which 
depends for such a distance inferiorly that the front margin 
actually exceeds the triturating surface in length. To give 
precise data, the total length in an antero-posterior direction is 
3.4 cm. ; length of triturating surface, 2.6 cm. (tritor, 1.5, cut- 
ting edge, 1.1) ; of anterior margin, 2.9 ; maximum thickness 
(width), 0.3 cm. Viewed from above, the curvature is seen to 
be only slightly sigmoidal and there is scarcely any thickening 
on the inner face at the symphysis. The tritoral puncte are 
- transversely directed, and the longitudinal ridge just back of 
the tritor nearly coincides with the median line. As is inva- 
riably the rule, beveling due to wear is confined to the inner 
face of the cutting edge. : 
The original of Figs. 37 and 39 belongs to Mr. Teller. Its 
outer wall is nearly straight for the greater portion of its length, 
but curves gently outward in advance of the tritoral area. This 
outward curvature is more strongly marked in another of Mr. 
Teller’s specimens, recalling that shown in Fig. 3. Below the 
cutting edge, in about the center of the bony substance form- 
ing the outer wall of the jaw, is to be seen a circular pit or 
indentation 0.5 cm. in diameter and 0.2 cm. deep (see Fig. 39) 3 
and as a similar depression occurs in the same region of 
another specimen, the outlines being quite regular in both, it 
appears to have been a natural cavity. All of the lower dental 
plates have an uneven grinding surface, the principal slope 
being downward and outward. Other species have the slope 
usually downward and inward. The tritoral puncte are nearly 
transverse in their direction, with a tendency toward forward 
and inward posteriorly. This is contrary to the conditions in 
the upper dental plates, which have the punctz directed forward 
and outward. The original of Fig. 37 shows two vertical lines 
on the inner face of the symphysis which bound an area of 
apparently denser structure than the surrounding tissue and 
has a separate system of vascular canals. The thickening at 
this region has been reduced through abrasion, but it is seen 
from another specimen that a vertical triangular depression 
