1864.] PROF. HUXLEY ON ARCTOCEBUS CALABARENSIS. 323 
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 ob- 
securely tuberculated, internally and externally. 
Each of the three molars has about the same length (0°15 inch) ; 
the two anterior ones are 0°1 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 in- 
terest, if one reflects how extensively this doubly crescentic pattern 
obtains among other Mammalia. And, again, the foregoing ana- 
lysis of the form of the molars shows that, different as the patterns 
of the grinding-surfaces of the upper and lower molars appear to 
be at first sight, they are really arranged upon much the same 
scheme. 
Furthermore the transition from premolar to molar is effected in 
the same way in the lower as in the upper molars —by the develop- 
ment of cusps which are rudimentary in the premolars, and by the 
appearance of an oblique ridge. 
The dentition of the genera Loris (Stenops), Nycticebus, Pero- 
dicticus, Otogale, Galago, and Otolicnus resembles that of the An- 
gwantibo in all essential particulars, but presents certain very inter- 
esting minor deviations. 
In Loris the third premolar differs much from the first molar in 
both jaws; and the last molar of the upper jaw has its internal 
posterior cusp well developed, so that it is quadricuspid. The last 
molar of the lower jaw is quinquecuspid. The oblique ridges of 
both upper and lower molars are well developed ; but, in the lower 
jaw, they do but just reach the anterior internal cusp. 
In Nycticebus javanicus the oblique ridges are well marked in the 
upper molars, sometimes less distinct in the lower ones. Out of four 
skulls, the inner posterior cusp of the hinder upper molar was obso- 
lete in three, and very small in the fourth. In the lower jaw, the 
fifth cusp of the last molar was very small or obsolete in three, while 
in the fourth (the same as that which had the inner posterior cusp 
of the last upper molar developed) it was distinct. 
The dentition of Perodicticus potto (fig. 4), it is important to note, 
differs more from that of the Angwantibo than either of the preceding. 
