205—28 INDIAN TERTIARY AND POST-TERTIARY YERTEBRATA. 
Dentition. — Regarding the cheek-teeth, and especially those of the upper jaw, 
it may be predicated of the entire group that the true molars are always 
two in number in the upper, and, with one exception, three in the lower jaw, 
but they vary very considerably both in the form of the outline of the crown, 
and in the relative degree of development of their four main cusps. In the 
upper jaw the outer pair of cusps, or lobes, are generally distinct, ■ while the inner 
pair are very generally confluent into an antero-posterior ridge. In Ursus the crowns 
of the upper true molars are always longer than broad, while in Bycenarctos they are 
generally more or less nearly square, but in some forms they have a tendency to the 
obliteration of the internal angles of the crown, and thus pass imperceptibly into the 
transversely elongated molars of Dinocyon and the true dogs : this subject will be 
more fully noticed in the sequel. 
Coming to the upper carnassial it will be found that, when known, this tooth is 
always of a more or less triangular form ; and that (with the exception of Mluropus) 
its ‘ blade ’ or outer portion, normally consists of two main cusps or lobes : in some 
genera, however, ( Bycenarctos ) an anterior cusp, or talon, is developed, partaking more 
or less completely of the character of a third lobe : the inner, or tubercular portion, 
normally consists of a single cusp : the relationship of the upper carnassial of 
Hycenarctos to that of the dogs will be noticed below. 
There is, however, another very important aspect in which the upper carnassial 
may be regarded. In classifying the dogs, Professor Huxley, as will be shown below, 
has arranged them according to the degree of development of the cheek-teeth in 
proportion to the size of the skull, and also to that of the upper carnassial to the true 
molars. With regard to the second relationship, it will be found that the present 
group may be arranged in two sections, accordingly as pm. 4 is smaller, or as large as, 
or larger than m. L The former section may be termed meionocreodonts, and the latter 
megalocreodonts , thus — 
Meionocreodonts Megalocreodonts 
Ursus. AEluropus. 
Arctotherium. 
Hycenarctos. 
Dinocyon. 
The following table gives the actual measurements of six species, viz.: — 
XJrsus 
labiatus. 
Ursus 
torquatus. 
Ursus 
arctos. 
JEluropus. 
Hysenarctos 
sivalensis. 
Dinocyon 
hemicyon. 
Length of pur 4 0 - 48 
6-48 
0-55 
1-0 
1-3 
(?) 1-2 
„ „ m.l 0-62 
0-78 
0-78 
0-88 
1*2 
0-85 
It will be seen from these dimensions, that although the members of the genus 
Ursus do not form a completely progressive series, yet that the whole number of 
genera shows a general advance in the relative degree of development of the 
upper carnassial from the true bears to Dinocyon, in which, however, the length of 
that tooth can be only approximately given. 
With regard to the true bears (Ursus) and their nearest allies (Arctotherium, 
