﻿14 PLEISTOCENE MAMMALIA. 



a double row of low cusps lying along the inner and outer edges of the tooth. Of 

 the four cusps along the outer border, the anterior and posterior are very small, 

 the second from the anterior end being the largest. The cingulum is well marked 

 along the inner surface. The tooth is fixed in the jaw by three roots, one lying 

 internally and the other two antero- and postero-externally. 



In bears of the arctos type the cingulum is less marked, and the two principal 

 cusps along the outer border do not appreciably differ in size. 



M. 2 is the largest tooth belonging to the molar series. The grinding surface 

 is completely tuberculated, the two most prominent cusps or elevations (W) occupy 

 the anterior half of the outer border, and behind them a third and much smaller 

 cusp is often found. The anterior cusp tends to be the largest. There are four 

 roots, one placed anteriorly, one near the middle of the outer surface, one postero- 

 internally, and one on the inner surface near the anterior end. 



In bears of the arctos type the two antero-external cusps tend to be equal in 

 size, and the tooth to narrow posteriorly more than in the cave bear. These 

 distinctions, however, do not always hold, and are of little practical value. 



(8) Permanent Dentition in the Lower Jaw (see PI. VI). — I. 1 is a small tooth 

 with both root and crown much laterally compressed. The crown forms a single 

 very slightly recurved cone, with a small tubercle on the outer side. I can detect 

 no valid difference in bears of the arctos type. 



I. 2 has the root similar to that of I. 1, but the crown is not so much 

 compressed and the tubercle on the outer side is larger and placed lower down 

 the crown than in L~T. There is also an indication of a tubercle on the inner 

 side of the crown, while from each tubercle a slight ridge rims downwards and 

 backwards to meet its fellow at the base of the crown. 



In bears of the arctos type the outer tubercle is relatively more prominent than 

 in U. spelsp.us, while the inner tubercle and pair of dowmwardly and backwardly 

 directed ridges are not present. 



I. 3 is a slightly larger tooth with the root triangular in section, the apex of the 

 triangle being directed backwards. The outer tubercle (PI. VI, fig. 2, e) is very 

 prominent and sharply divergent from the crown. A slight ridge passes backwards 

 and downwards from it to meet another bounding the inner side of the crown. In 

 bears of the arctos type the tooth differs only in its smaller size, and in the slighter 

 development of the ridges. 



C. This tooth differs from the corresponding one in the upper jaw in having 

 sometimes at any rate, both crown and terminal part of the root slightly inwardly 

 inflected on the main part of the tooth. The smaller size is the only respect 

 in which c. of bears of the arctos type differs from the corresponding tooth of the 

 cave bear. 



I'm. ], 2, 3, which are absent as a rule in the cave bear, are all small conical 



