1916] Merriam-Stock— Moody : An American Pliocene Bear 95 



Considering that in no. 22362 M- is considerably worn, and allow- 

 ing for individual variation, the resemblances between the Oregon 

 specimen and the type of I. salmontanus are close. Small differences, 

 such as the more distinctly circular cross-section of the metacone, the 

 smaller hypocone, .slightly longer heel, and wider trigon region in 

 the Oregon form, suggest specific distinction such as would be expected 

 in individuals so widely separated geographically. 



The characters of M- in the Oregon form, and in Inclarctos salmon- 

 la n us, approach those of Hyaenarctos excepting in relative elongation 

 of the heel. The two outer cusps of M- in Hyaenarctos may show 

 somewhat stronger lateral compression than is noted in the Oregon 

 form. The antero-internal ridge in Hyaenarctos may apparently show 

 almost no separation into two divisions, or may be very distinctly 

 divided as in H. palaeindicus, in which the hypocone region is imper- 

 fectly developed. In H. punjabiensis (fig. 11) an incipient heel is 

 clearly shown, though it is much less pronounced than in Imlarctos. 

 As has been suggested by Pilgrim, an intermediate stage between the 

 form seen in H. punjabiensis and that in the type of 7. salmontanus 

 might connect the two groups so closely that generic separation would 

 be difficult if not impossible. 



M- of the Rattlesnake specimen is distinguished from that of 

 Arctotherium by its greater width and much shorter talon. In 

 Arctotherium the primitive quadritubercular portion of the tooth is 

 longer anteroposterior^ and the heel is much longer. The arrange- 

 ment of the tubercles is much the .same in the two types, hut the 

 tubercles show stronger lateral compression in Arctotherium. 



The arrangement of the roots supporting M- in the Oregon speci- 

 men differs somewhat from that in Arctotherium simum. In no. 22362 

 (fig. 8rt) there are two distinct external roots supporting the paracone 

 and metacone regions. These roots in both available teeth are dis- 

 tinct, but are not widely separated. The inner and posterior regions 

 of these teeth are supported by a large, broad root evidently composed 

 of two parts, one of which supports the protocone region and the other 

 originates above the hypocone and the region behind it. 



In Arctotherium there are also evidently four original root 

 elements, but the roots beneath the paracone and metacone tend to 

 diverge widely, the element above the metacone being in some cases 

 united with the posterior root supporting the heel. In Arctotherium 

 the root supporting the protocone may or may not unite with the root 

 above the heel. In the type of Imlarctos salmontanus the roots are 

 not exposed. 



