P. N. Bose—History of the Extinet Carnivora. 273 
remains, was of moderate dimensions; the three molars, which are 
all well preserved, are constructed on essentially the same pattern 
as the corresponding teeth of Gymnura. In Amphicyon the sectorial 
is better developed, and the length occupied by the molar series 
behind the sectorial proportionately lessened ; first by diminution 
in size of the hindermost molar; and, secondly, by the first and 
second molars losing their primitive quadrangular structure, and 
becoming longer transversely than antero-posteriorly. In Cynodon the 
sectorial is still more differentiated than in Amphicyon, and the 
space occupied by the true molars correspondingly shortened, the 
last molar being altogether absent in some species constituting the 
subgenus Oynodictis. The upper-jaw teeth of Arctoycon, Amphicyon, 
and Cynodon, besides agreeing in numberand general form and arrange- 
ment, have this important point of resemblance in common, viz. 
that there is one tooth more or less differentiated as a flesh-cutting 
tooth, and that the three teeth behind it preserve more or less of 
their primitive structure, and may be properly called ‘“ tuberculous.” 
But in Proviverra, Hyenodon, and Pterodon of the European Kocene, 
and Ambloctonus, Oxyena, and Stypolophus of the Lower Eocene of 
New Mexico, there is a succession of three or four similar teeth having 
the form of the sectorial. In Ambloctonus all the three true molars 
have this form; in Proviverra, as well as Stypolophus, the hinder- 
most molar has become transverse; and Ozyena differs from 
Stypolophus (= Proviverra) only in having one molar less. The 
upper-jaw teeth of Pterodon and Hyenodon are constructed on the 
same type as those of Proviverra, only the last molar is propor- 
tionately more reduced in size in Pterodon, and is generally absent 
in Hyenodon.' The presence of several “sectorials” has been re- 
marked by Prof. Gaudry to be “peculiar to the Marsupials.” But. 
as we have noticed above, it is very common amongst the Insecti- 
vores (e.g. Talpa, Centetes, Glisorex, etc.). There is, however, ore 
fatal objection to the institution of a comparison between the molars 
of the Eocene Carnivores mentioned above and those of Thylacine 
or Dasyure; and that objection will be noticed, after we have ex- 
plained the most important points in the dentition of the lower jaw. 
(B.) Lower Jaw.—In Gymnura, the incisors are smaller than in 
the upper jaw, and the canine proportionately larger, stronger, and 
more recurved, attaining in Centetes, as in the upper jaw, the typical 
form and dimensions of the Carnivora. The premolars are conical 
and trenchant; the first two are small and simple, the third and 
fourth considerably larger, and the latter with rudimentary anterior 
and posterior cusps. The true molars are all quadricuspidate, de- 
creasing in size from the first to the third. The structure of the 
first molar is most instructive. The anterior pair of cusps is more 
elevated than the posterior; the cingulum from the external border 
of the tooth is produced forward and inward, and the cingulum from 
the internal border is slightly produced so as to meet its fellow from 
1 Prof. Gervais (op. eit. p. 232) is of opinion that there is a very small molar 
behind m. 2 in H. leptorhynchus. 
DECADE II.— VOL. VII,.—NO. VI. 18 
