322 PROF. HUXLEY ON ARCTOCEBUS CALABARENSIS. [June 28, 
cusp; while the cingulum itself is produced internally and behind 
into a third similar cusp. Thus the second and third premolars are 
tricuspidate, two cusps being internal and one external; the ridge 
which runs down the inner face of the latter joins the antero-internal 
rudimentary cusp. 
The two anterior molars (4, 5) are larger than the premolars, mea- 
suring 0°15 inch long by 0°18 wide. The hindermost (6), on the 
other hand, is hardly larger than the last premolar, being 0°1 inch 
long by 0°13 inch wide. 
The two anterior molars are each surrounded by a cingulum, like 
the premolars, but are quadricuspidate. As in the premolars, the 
outer cusps are larger than the inner; but the disproportion is far 
less. The last molar has the postero-internal cusp rudimentary. 
If the crowns of the molars and premolars be compared together, 
it will be found that the former differ from the latter, mainly, in the 
great relative development of the parts answering to the posterior 
basal process and the rudimentary cusps of the premolars. 
Of the two outer cusps of the molars, the anterior represents the 
principal cusp of the premolars ; the posterior is an additional growth 
from the outer side of the heel, which has now become as large as 
the anterior division of the tooth. The two inner cusps are readily 
identifiable with the rudimentary cusps of the premolars, the only 
important difference being that the antero-internal cusp is now sepa- 
rated by a groove from the cingulum, instead of rising directly from 
it. The oblique ridge connecting the antero-internal with the postero- 
external cusp appears to be a new development, not represented in 
the premolars. By its appearance, the molars of the Angwantibo ac- 
quire the pattern which is so obvious in Man and in the Anthropo- 
morpha, but which is absent in all the Old-World Apes and in most 
of those of the New World. : 
In the lower jaw (B, D, fig. 3) the proclivous, close-set incisors and 
canines occupy a space of 0'15inch. The grinding series is 0°7 inch 
long; and the first premolar is separated from the second by an in- 
terval 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 con- 
vex 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 0°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, trace- 
able on both the inner and outer faces, rises much higher in front 
than behind, and is produced posteriorly into a slight cusp-like 
