De la BECHE and CONYBEARE, 1821

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 subsequently 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 growing up in the interior of the cavity of the old one, and when matured, 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 other 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 Ichthyosaurus 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.