260 ON PLATYGONUS COMPRESSUS : 



rounded angles ; the crown rises externally into a subquadrangular 

 tubercle, which is impressed anteriorly and posteriorly ; the external 

 surface of this elevation is continuous with the margin of the tooth, 

 while on the other sides it is surrounded by a broad cingulum, which 

 is wider posteriorly. In the younger individual (fig. 2), this cingu- 

 lum rises into an acute ridge, which is foveate on the anterior and 

 interior portions. 



The second premolar, ;7. 2 (figs. 2 and 12), is subtriangular, slightly 

 transverse, with a large transverse elevation, and an anterior and 

 posterior basal margin, which nearly unite on the external face in 

 the younger specimen. The transverse elevation is divided into two 

 cusps, by a deep antero-posterior incision, and the posterior basal 

 margin, at the external angle, rises into a small tubercle. 



The third premolar, left side, p. 3 (figs 2 and 13), is subquadrate, 

 transverse, and a little narrowed internally ; it is furnished with 

 transverse elevation and basal margins, as in the preceding, but they 

 are more strongly marked : the external pyramid is slightly pro- 

 duced anteriorly, and descends almost to the margin of the tooth. 



The fourth premolar, left side, p. 4 (fig. 13), is similar to the molar 

 next described in all its sculpture, but is smaller, and the shape 

 slightly different ; the internal margin is scarcely emarginate, and 

 the anterior margin is not oblique, but very slightly sinuous, for the 

 curve of the 3d premolar. 



The first molar, m. 1 (fig. 13), is quadrate, with two large trans- 

 verse elevations, each of which is divided into two pyramids, or 

 cusps, the external being smaller ; the internal posterior pyramid is 

 produced obliquely outwards to the posterior margin ; the internal 

 anterior pyramid sends a similar but smaller prolongation to the 

 anterior margin. The basal cingulum is well developed on the 

 anterior, external, and posterior margins, except where it is sub- 



