300 



Sp II. /. tenuirostris. — The apex of the teeth is more elon- 

 gated and more acute. The head, figured in the 

 Philosophical Transactions for 1820, PI. xv. be- 

 longs to it. 

 Sp. III. /. platyodon. — The teeth are more flat and smooth 

 than in the former species. It is not yet figured. 

 All these species, in which the teeth form the most 

 obvious distinguishing mark, are found in the lias ; one 

 other species, at least, is found in the Kimmeridge clay, 

 and is sufficiently characterized by the contour of the 

 cervical vertebrae, but the difference would not admit of 

 description in an elementary work. The remains of the 

 ichthyosaurus are also found in the calcareous grit under the 

 coral rag, and in clay above the iron sand ; so that it may- 

 be considered as common to all the beds between the red 

 marl and green sand, or perhaps chalk. 



Plesiosaurus.* — Mr. Conybeare observes, he has nothing 

 to add here to the generic description given in the paper in 

 the Geological Transactions, except that the dentition 

 appears to have been as in crocodiles, and the teeth to be 

 placed in alveoli.f 



* YlKvi(TiO(7^ approximate to, and 'EccvpOd, a lizard. 



"t" To render the present account more perfect, it has been 

 thought proper to introduce, from the paper of Messrs. de la Beche 

 and Conybeare, the following abridged account of their obser- 

 vations : — 



"The newly-discovered animal adds another to that family, 

 which, approaching closely to the lizard family, and especially to 

 the genus crocodile, differs from it in many important characters, 

 especially in the structure of the paddles, which possess an inter- 

 mediate structure between the feet of quadrupeds and the fins of 

 fishes, and approach in many respects, most nearly to the paddles 

 of turtles. 



"This animal appears to be intermediate between the crocodile 

 and ichthyosaurus ; but whilst the ichthyosaurus recedes from the 

 forms of the lizard family, and approaches those of fishes, the new 



