600 ON ARCTOCEBUS CALABARENSIS 
inch long; and the first premolar is separated from the second 
by an interval about equal to that which exists between it and the 
canine. 
The incisors are laterally compressed, and, at their bases, longer 
from before backwards than they are from side to side. Their front 
faces are convex from above downwards ; their posterior faces convex 
from side to side, but concave from above downwards, and so 
inclined to the front faces that the upper rounded edges are sharp. 
The canines are like the incisors, but somewhat broader, thicker, 
and sharper at the edges. The cingulum of the incisors and canines, 
unmistakeably present, and, in its ordinary place on the backs of the 
teeth, becomes confounded with their outer edges higher up, so that 
their front faces might be said to be almost wholly, if not quite, 
* subcingular.” 
The first premolar has the crown o'17 inch long, and therefore is 
a much larger tooth than the canine. It is recurved and pointed, 
and has a sharp anterior and posterior edge; the cingulum, traceable 
on both the inner and outer faces, rises much higher in front 
than behind, and is produced posteriorly into a slight cusp-like 
talon. The inner face of the tooth has an obscure rounded longitu- 
dinal ridge. 
In the other two premolars, which are successively shorter than the 
first, the form of the tooth is fundamentally similar; but the base 
becomes broader, the inner ridge more definite and slightly angulated, 
and the posterior basal process of the tooth more distinct, and 
obscurely tuberculated, internally and externally. 
Each of the three molars has about the same length (0°15 inch) ; 
the two anterior ones are ol inch broad and quadricuspidate ; the 
last, a little narrower, is quinquecuspidate ; the fifth tubercle being 
median and_ posterior. 
A well-marked transverse ridge connects the antero-external with 
the antero-internal, and the postero-external with the postero-internal 
cusp ; and besides these an oblique curved ridge connects the postero- 
external with the antero-internal cusp. The cingulum is well deve- 
loped, and there is an anterior basal process, whence a ridge rises 
to the antero-external cusp. 
This ridge and the oblique ridge before-mentioned so connect the 
other ridges and cusps, that the grinding face of the tooth exhibits 
an almost doubly crescentic pattern—a circumstance of no small 
interest, if one reflects how extensively this doubly crescentic pattern 
obtains among other Mammalia. And, again, the foregoing analysis 
of the form of the molars shows that, different as the patterns of the 
