62 



A basal ridge exists at the outer back pari of the crown of the second pre- 

 molar, and, less produced, exists in (lie same position in the third. No ridge 

 occupies the inner prominence of the inner lobe of the second premolar. 



A specimen of an upper left last premolar, found at Grizzly Buttes by Dr. 

 ( 'orson, is represented in Fig. 12, Plate IV. It is larger than in the entire series 

 of Fig. 10 and is less worn. It exhibits a basal ridge externally interrupted 

 at the middle ; and internally the ridge is also interrupted or nearly obsolete 

 at the middle. The posterior ridge or fold between the inner and postero- 

 external lobes, though smaller, is more defined from the lobes than the ante- 

 rior ridge. The latter appears rather as a prolongation of the inner'lobe to 

 the fore part of the base of the antero-external lobe. The posterior ridge has 

 the appearance of an introduced piece defined from the lobes by constrictions 

 or grooves. The arrangement is badly represented by the artist ; nor is it 

 obvious if it existed in the corresponding more worn tooth of the series of 

 Fig. 10. 



In a much mutilated specimen, obtained, by Dr. Corson at Grizzly Buttes, 

 containing the remains of the last two premolars and succeeding two premo- 

 lars, the basal ridge is better developed at the inner part of the crown than 

 in any of the preceding. The last premolar exhibits the same condition of 

 the posterior ridge intervening to the internal and postero-external lobes of 

 the crown as that described in the isolated tooth. The same tooth, barely 

 worn, exhibits the summit of the inner lobe of the crown slightly divided into 

 two points, so that it presents a less degree of connation than in the preceding 

 specimens. 



The upper molars and premolars, except the first one, are inserted by three 

 fangs, of which the inner one is a connate pair; the connation being most 

 complete in the premolars. The first premolar has two fangs. The space 

 occupied by the upper molar series is about 3f inches. 



Fig. 13, Plate IV, represents a specimen, found by Dr. Carter, in company 

 with the upper molar teeth of Figs. 9 and 10, and evidently pertaining to the 

 same individual. The specimen consists of the anterior extremity of the 

 lower jaw, retaining the incisive alveoli, the canines, and on one side the four 

 premolars. A view of the triturating surfaces of the latter is given in Fig. 

 14. Figs. 15 and 16 represent a second molar, and Fig. 18 an incisor from 

 the same individual. 



Fig. 25, Plate XX, was drawn from a specimen consisting of the greater 



