564 Mr. De la Beche and Mr. Conybeare on 
whole structure, it will not be found to possess analogies sufficiently 
numerous or strong with the peculiar organisation of the Proteus to 
authorise the change of this appellation into Proteosaurus, as sub- 
sequently proposed. 
Particular Observations . 
Osteology of the Head . 
a. Teeth.* These bear a near resemblance in form to those of 
the crocodile ; and the mode of dentition by the young tooth grow- 
ing up in the interior of the cavity of the old one, and when ma- 
tured, splitting and causing it to fall, is exactly similar. 
The teeth are more numerous than in the crocodile ; there cannot 
be less than 30 on a side in either jaw : but from their irregular 
growth, their partial concealment in the stone, and difficulty of 
finding complete jaws, they have not yet been accurately numbered. 
They are placed in a long sulcus, formed in the maxillary and 
intermaxillary bones, like that in the jaw bones of some fishes, not 
in separate alveoli, as in the crocodile. 
b. Lower Jaws . In order to demonstrate the close relation 
between the Ichthyosaurus and the lacerta family, it is necessary to 
premise, that the lower jaw in that order, instead of having, like 
mother quadrupeds, a single bone on either side, exhibits no less than 
six of these ; one called the dental, which carries the teeth, forms 
the whole anterior extremity of the jaw, and continues to cover the 
* From the different forms of the teeth alone, three species at least of the Icthyosau- 
«rus may be ascertained ; but they differ only in very slight points, and not in any that 
very materially affect the general form and structure of parts to which it is our intention 
to confine ourselves in the present paper. Hereafter we propose a further communication 
on this subject. 
