60 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 20, 



from the first premolar. In the upper jaw the canine is separated 

 by a rather wider space than in the lower jaw from the incisors, and 

 by a rather narrower space from the premolars. In thickness of 

 base and, apparently, in length and shape of crown, the upper canines 

 resembled the lower ones. The premolars, p, and molars, m, form a 

 continuous series on each side of both jaws ; except that a space of 

 about a line intervenes between the first and second premolars in the 

 lower jaw. 



The premolars increase in size and complexity to the fourth, which 

 nearly equals that of the true molars. The last of these, m 3, in the 

 lower jaw, presents a third lobe. In PI. II. fig. 3, the premolars of 

 the upper jaw are marked 1, 2, 3, 4 : the true molars of the lower 

 jaw are marked 1, 2, 3 : the dislocation of the jaw carries these one 

 tooth in advance. In the upper jaw, the first premolar, PI. II. fig. 3, 

 p 1, presents the common subcompressed conical shape, with the 

 base of the crown swelling out below the fangs, and the protuberant 

 part continued along the outside of the middle part to the apex of 

 the cone ; on each side of this prominence the crown presents a de- 

 pression ; and the surface, though polished, is broken by a few irre- 

 gular longitudinal indentations, which give the enamel a slightly 

 wrinkled character. 



The second premolar, p 2, resembles the first ; but is somewhat 

 larger, especially thicker, and with the front and back parts of the 

 base more produced; an outer longitudinal groove near the summit 

 of the cone indents it deeply. 



The third premolar, p 3, has two cones on the outer side, and an 

 anterior basal talon ; from this a slight ridge is continued upon the 

 outer part of the anterior cone : the whole outer base of the poste- 

 rior cone is girt by a similar low cingulum, continued into a rudi- 

 mental talon behind. The crown expands posteriorly, and its work- 

 ing surface is increased by an internal ridge, and the valley dividing 

 it from the two outer cones. 



In the fourth premolar, the crown, PI. III. figs. 1 & 2, p 4, with 

 an increase of thickness, presents greater complexity : the cingulum 

 is uninterrupted along the outer side from its anterior well-developed 

 talon, c f , to the back part where the ridge, t, represents the talon. 

 The two outer cones resemble those of the true molars ; but there is 

 only one inner cone, and the crown of p 4 differs accordingly from 

 that of m 1, in being triangular rather than square. A ridge, r, is 

 continued from the interspace between the anterior talon, c\ and the 

 outer anterior lobe obliquely inward and backward to the inner 

 lobe, swelling into a small tubercle at the middle of its course ; a 

 lower rising, hardly to be called a tubercle, intervenes between the 

 inner cone and the outer posterior cone. The cingulum forms a 

 well-marked ridge, t> along the back part of the crown, and is con- 

 tinued more feebly round the base of the inner lobe, with a brief in- 

 terruption at its most prominent middle parts : beyond this the 

 cingulum is continued into the anterior basal ridge, which expands 

 into the small antero-external basal tubercle, c 1 . The fourth upper 

 premolar is implanted by two external and one internal roots. 



