474 DESCRIPTION OF A FRAGMENT OF 



certa Linn.), since in all that family, except the crocodile 

 and the Saurian of Luneville discovered by Dr Gaillardeau, 

 the teeth are not lodged in alveoli, or even in a continu- 

 ous furrow ; on the contrary the jaw bone presents only a sort 

 of parapet on the outer side — the teeth are fixed to the jaw 

 by a bony mass, occupying the place of their root, and incor- 

 porated organically both with the tooth and with the jaw 

 bone — and the new teeth make their first appearance in cells 

 from within this osseous mass, and shoot irregularly through 

 its substance, gradually producing a necrosis in it, thus 

 causing both the mass and the old tooth to fall out. 



This animal differs from the crocodile in the composition 

 of its jaw, in the form and position of its teeth, in the mode 

 in which the nerves and blood vessels are transmitted to the 

 teeth, &c. &c. It differs from the Saurian of the environs 

 of Luneville in the form and character of the teeth, which 

 in the latter are conical, strongly striated, and alternately 

 larger and smaller — also in the mode in which the blood 

 vessels are transmitted to the teeth, &c. 



It most probably belongs to the order Enalio Sauri of 

 Conybeare ; an order formed for certain animals which ap- 

 proaching more closely to the Saurian or Lizard family, and 

 especially to the genus Crocodile, than to any other recent 

 type, yet recede from it in many important characters, es- 

 pecially in the form of their paddles, which possess an inter- 

 mediate structure between the feet of quadrupeds and the 

 fins of fishes*. 



It is impossible, however, to place the animal which forms 

 the subject of this communication in any of the hitherto 

 described genera of this order. It is excluded from the 

 genus Ichthyosaurus by the composition of its jaw ; by the 

 teeth in the latter being placed in a sulcus and not in dis- 

 tinct alveoli, and also by the nerves and blood vessels being 

 transmitted to the teeth of the lower jaw by perforations on 

 the outside of the anterior portion of the dental bone, &c. 



* See Geological Transactions, Vol. I. N.B. p. 561. 



