368 , BRITISH FOSSIL REPTILES. 



figs. 6, 7, and 8) deviate too much from those of the Crocodilian family to make at all 

 probable a reference of them to the genera Poikilopleuron, Streptospondylus, or Cetio- 

 saurus, which are much more closely allied to the Crocodilians than is the H3'l0eosaurus. 

 In a later work,* Dr. Mantell attributes these teeth, on the authority of M. Boue, to 

 the Cylindricodon, a name by which Dr. Jiiger distinguishes one of the species of his 

 genus " Phy tosaurus." I have been favoured by Dr. Jiiger with one of the bodies supposed 

 to be the teeth of the Cylindricodon of the Wirtemberg Keuper, but it is merely the 

 cast of a cylindrical cavity, consisting entirely of that mineral substance, without a 

 trace of dental structure. The difference of form between the Wealden teeth now 

 under consideration, and those on which the PJii/fosaurus cylindricodon of Jiiger was 

 founded, is pointed out in detail in my ' Odontography,'! and has been likewise appre- 

 ciated by the estimable palaeontologist, M. Fischer de Waldheim, by whom their 

 resemblance to certain Saurian teeth from the Ural Mountains, belonging to the genus 

 Rhopalodon, is indicated. From these teeth, however, the presumed Hyteosaurian 

 teeth differ in having thick and flat instead of serrated coronal margins. 



The fang of the tooth is subcylindrical, subelongate, smooth ; as it approaches the 

 crown it diminishes in one diameter, and slightly and gradually expands in the oppo- 

 site diameter, forming a sub-compressed, slightly incurved crown, with the borders 

 straight and converging at a moderately acute angle to the apex. These borders, in 

 most specimens, are more or less worn, indicating the teeth of the opposite jaws to 

 have been placed alternately, so as to meet and reciprocally occupy the angular 

 vacuities left by the sloping borders of the crown : the enamel at these borders being 

 worn away, and the dentine exposed. 



The following is the result of a microscopical examination of these teeth. The 

 tooth consists of a body of dentine covered by a thick coating of clear enamel, with 

 minute superficial longitudinal striae, and surrounding a small central column of osteo- 

 dentine, consisting of the calcified remains of the pulp. The dentine differs, like that 

 of existing Lacertians, from the dentine of the Iguanodon in the entire absence of the 

 numerous medullary canals which form so striking a characteristic of the more gigantic 

 Wealden reptile. The main dentinal tubes are characterised by the slight degree of 

 their primary inflections ; they are continued in an unusually direct course from the 

 pulp-cavity to the outer surface of the dentine, at nearly right angles with that surface, 

 but slightly inclined towards the expanded summit of the tooth. They are chiefly 

 remarkable for the large relative size of their secondary branches, which diverge from 

 the trunks in irregular and broken curves, the concavity being always towards the 

 pulp-cavity. In most parts of the tooth, the number of these branches obscures even 

 the thinnest sections. 



* • Geology of the South-east of England,' p. 293. 

 t P. 196. 



