WEALDEN FORMATIONS. 21 



Teeth of the Hylaosaw ? T. VIII, figs. 6—9- 



At the period of preparing my ' Report on British Fossil Reptiles,' the teeth of the 

 Hylaeosaurus were unknown ; but in the quarries where the bones of that reptile had 

 been discovered, a few teeth had been met with of a peculiar form, respecting which 

 Dr. Mantell wrote — "They appear to have belonged to a reptile, and are entirely 

 distinct from those of the Megalosaurus, Iguanodon, Crocodile, and Plesiosaurus, whose 

 remains occur in the Tilgate strata."* The form and structure of these teeth (T. VIII, 

 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 Hylteosaurus. 

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

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

 genus " Phytosaurus." I have been favoured by Dr. Jager 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 Phytosaurus cylindricodon of Jager 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 Hylaeosaurian 

 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- 



* 'Wonders of Geology,' vol. i, p. 403. 



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



X P. 196. 



