230 ON THE EXTINCT MAMMALIA OF 



Rhinoceros hesperius. 



The remarkable discovery of remains of several species of Ithinoceros in Dakota, 

 Nebraska and Texas — a genus which previously was supposed to have been peculiar to 

 the eastern hemisphere — has been followed by the further discovery of the remains 

 of a species, apparently diflferent from any of the preceding, west of the Rocky Moun- 

 tains. Prof. J. D. Whitney, engaged in a geological survey of California, has sub- 

 mitted to my inspection a portion of the lower jaw of a Rhinoceros, derived from a 

 tertiary deposit of Chili Gulch, Calaveras Co., California. 



The specimen so closely resembles in its general aspect and state of petrifaction the 

 Mauvaises Terres fossils of White River, Dakota, that it would have been viewed as 

 one, if the locality from which it was obtained were not known. It consists of the 

 right side of the lower jaw, without the ascending portion, and with the symphysial 

 portion of the opposite side. It contains the true molars, the fangs of four premolars, 

 one lateral incisor and the fang of the other, and the alveoli of the internal incisors. 

 The specimen is represented, reduced one-half, in figures 11, 12, plate XXIII. 



The form of the jaw is nearly like the corresponding portion in the Indian Rhino- 

 ceros, and the formula of dentition is the same as in this species. It indicates a 

 species nearly the size o^ Rhinoceros occidentalis. Compared with the lower jaw of the 

 latter-, its body has a considerably greater depth in relation with the size of the con- 

 tained molar teeth, and the chin is of much more robust proportions, in accordance 

 with a greater degree of development of the incisors. The symphysis is fifty-two 

 lines in length ; the width of the chin at the middle twenty-nine lines. The hiatus 

 separating the molars and incisors has a prominent acute edge, and measures two and 

 a half inches in length. 



The molar teeth undergo a more rapid reduction in size, advancing through the 

 series, than in R. occidentalis. While the true molars average the size of those of the 

 latter, or are intermediate in size to those of two specimens of the lower jaw of -B. 

 occidentalis, the premolars are proportionately much smaller. 



The whole series of six large molars in the California Rhinoceros measures seventy- 

 eight lines in length, and the average depth of the jaw below those teeth is about 

 thirty-two lines. In two lower jaws of R. occidentalis the corresponding molar series 

 measures in one case seventy-three lines long, and in the other ninety lines, and the 

 average depth of both jaws below these teeth is twenty-four lines. 



The true molar series in the California Rhinoceros occupy a space of forty-eight 

 lines; the three large premolars a space of thirty lines. Of the two jaws oi R. occi- 

 dentalis, in one case the true molars occupy a space of forty-two lines, the premolars 

 thirty-one lines ; in the other case the true molars occupy a space of fifty-two lines 

 and the premolars forty-one lines. Thus in the California Rhinoceros the premolars 



