MANDIBULAR EAMUS OF ANTHRACOSAURUS RUSSELLI. 887 



the sides, and is therefore in cross section somewhat angulated ; 

 and at the base it is wider in the transverse than in the longitu- 

 dinal direction of the jaw. The whole surface is covered with 

 brilliant enamel, and is longitudinally grooved to within less 

 than a third of the apex. The grooves are fine, rather distant, 

 and the spaces between them are flattened, so that there is a 

 tendency to a ridged appearance. 



The teeth are clustered, and in this respect agree with those 

 of the maxillae. In the clusters the bases are in contact ; and 

 short spaces divide the clusters. The first tooth (g) is split lon- 

 gitudinally by the anterior fracture of the specimen, and very 

 little of it remains : only a small piece of the base is perceptible ; 

 but a partial impression of the crown shows that it was as large 

 as the others. The base of the second tooth is not far from that 

 of the first, and is the first perfect one of the series. The third 

 tooth has been removed for structural examination ; it stood 

 apart, about a quarter of an inch from the second, and as far 

 from the fourth tooth. The fourth and fifth are in contact, and 

 are separated from the sixth by about a quarter of an inch ; the 

 sixth, seventh, and eighth are close together, and form the 

 largest cluster of the series. Then follows a space of upwards 

 of a quarter of an inch, and the series is terminated by three 

 teeth much smaller than the rest ; these are clustered, the first 

 two being almost perfect, and the third (A) having almost en- 

 tirely disappeared. These three posterior teeth are placed just 

 at the point where the alveolar border begins to rise, and are 

 two inches and a half from the hinder extremity of the specimen. 



The mandible of Anthracosaurus is distinguished from that of 

 Loxomma, the only known jaw with which it is likely to be con- 

 founded, not only by its greater size, but also by the massiveness 

 of the bone. It is an inch deeper or wider than the largest 

 mandible we have seen of the latter, and the bone is very much 

 thicker. The form of the teeth likewise distinguishes this species 

 from Loxomma: they have the crown much less compressed, 

 and the trenchant margins are not nearly so much developed ; 

 towards the base, too, they are more cylindrical, or rather 

 conical, though they are somewhat irregularly flattened and 



