PLESIOSAURUS. 159 



Head* 



The head of the P. Dolichodeirus exhibits a combination 

 of the characters of the Ichthyosaurus, the Crocodile, and 

 the Lizard, but most nearly approaches to the latter. It 

 agrees with the Ichthyosaurus in the smallness of its nostrils, 

 and also in their position near the anterior angle of the eye ; 

 it resembles the Crocodile, in having the teeth lodged in dis- 

 tinct alveoli ; but differs from both, in the form and short- 

 ness of its head, many characters of which approach close 

 ly to the Iguana.f 



lias at Street, near Glastonbury. At PI. IG is also copied Mr. Conybcare's 

 restoration of tliis animal, from dislocated fraornents, before any entire 

 skeletons were found, Tiic near approach of this restoration to the charac- 

 ter of the perfect skeletons, affords a striking example of the sure grounds 

 on which comparative anatomy enables us to reconstruct the bodies of fossil 

 animals, from a careful combination of insulated parts. The soundness of 

 the reasoning of Cuvier, on the fossil quadrupeds of Montmartre, was esta- 

 blished by the subsequent discovery of skeletons, such as he had conjectu- 

 rally restored from insulated bones. Mr. Conybearc's restoration of the Ple- 

 "siosaurus Dolichodeirus, (1*1. 16,) was not less fully confirmed by the speci- 

 mens above-mentioned. 



* See PI. 16, 17,18. 



t Mr. Conybeare, in the Geol. Trans, second series, vol. 1, part 1, PI. 

 19, has published figures of the superior and lateral view of a nearly perfect 

 head of this animal. Our figure, PI. 18, Fig. 2, represents the head of the 

 specimen in the British Museum, of which the entire figure, on a smaller 

 scale, is given in PI. 16. The head is in a supine position; the upper jaw 

 is distorted, and shows several of the separate alveoli that contained the 

 teeth, and also the posterior portion of the palate. Tlie under jaw is but 

 little disturbed. 



A figure of another lower jaw is given at PI. 18, Fig. 1, taken from a spe- 

 cimen also in the British Museum, found by Mr. Hawkins, at Street. 



PI. 19, Fig. 3, represents the extremity of the dental bone of another 

 lower jaw, in the same collection, retaining several teeth in the anterior 

 sockets, and also exhibiting a series of new teeth, rising within an inte- 

 rior range of small cavities. This arrangement for the formation of new 

 teeth, in cells within the bony mass that contains the older teeth, from 

 which they shoot irregularly forwards through the substance of the bone, 

 forms an important point of resemblance whereby the Plesiosaurus as- 



