236 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



ridges down the enamelled face, and the denticulated lateral 

 margins, and finely serrated edge of the summit, as seen in 

 the specimen figured in Lign. 50 . The shank, or fang of the 

 tooth partakes of the general form of the crown : it is slightly 

 curved, rather flat anteriorly, and convex on the opposite 

 face, and flattened or compressed at the sides ; it gradually 

 diminishes in size towards the base, and terminates in a 

 point ; a tooth of this kind in Case C, exceeds 2 \ inches in 

 length. 



There is considerable variation in the form of the summit 

 of the crown; in the upper teeth it is as angular as in the 

 recent Iguana. (Lign. 49, fig. 4.) The inner surface of the 

 crown in the lower teeth, and the outer surface in the upper, 

 are covered with a thick layer of enamel, but the sides and the 

 alveolar face of the crown have but a thin coating of this 

 substance. 



Specimens with the coronal aspect in its normal state are 

 but rarely met with, for the apex of the tooth is almost 

 always 'worn away, and the crown presents an oblique, trian- 

 gular, smooth surface, as in the beautiful example (in my 

 collection) figured in Lign. 51, which shows the anterior and 

 posterior aspect of a lower molar, found imbedded in the stem 

 of a Clathraria Lyellii (see ante, p. 45), as if the tooth had been 

 snapped off while the animal was in the act of gnawing the 

 tough vegetable trunk. This fossil affords an excellent illus- 

 tration of the form of the coronal part of a mature molar, the 

 apex of which is but slightly worn away. 



The lower part of the root is broken off ; in teeth of this 

 kind the fang generally terminates in a point, as in a specimen 

 partially imbedded in a block of Tilgate grit, on the middle 

 shelf of Wall-case C. The apex is worn down obliquely 

 (fig. 2. &.). The lateral denticulations, which are so peculiar 

 a character of these teeth, are well developed: when seen 

 in front, as in fig. 1, a, they appear as mere serrations, but 

 viewed laterally, they are found to be produced by a series 

 of denticulated plates. A transverse section of a tooth 

 of this kind exhibits a simple pulp-cavity in the centre of 

 a body of dentine permeated by calcigerous tubes ; with 

 this peculiarity, that the dentine is traversed by medullary 

 canals, which radiate at definite intervals from the centre 

 towards the periphery of the tooth ; the dentine of the Igua- 



