ON ARCTOCEBUS CALABARENSIS $99 
lum much more marked, and so greatly developed backwards as to 
give rise to a “ talon” (heel, or posterior basal process). From within, 
or above (fig. 3, C), the cingulum appears still better developed, in 
accordance with the increased breadth of the base of the tooth. The 
base of the first premolar (1) is not much thicker than that of the 
canine (0'083); but in the second (2) it measures o'r inch, and in the 
third (3) 0113 inch, In this last tooth, therefore, the crown is rather 
wider than it is long. Opposite the end of the ridge on the inner 
surface of the principal cusp, which is present in the premolars, as in 
the canine, rises, within the cingulum, a second, minute or rudimentary 
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, 
measuring O15 inch long by o18 wide. The hindermost (6), on the 
other hand, is hardly larger than the last premolar, being o1 inch 
long by 013 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 
separated 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 bea new development, not represented 
in the premolars. By its appearance, the molars of the Angwantibo 
acquire 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 
incanes occupy a space of o15 inch. The grinding series is 0-7 
