﻿MONOGRAPH 



OF 



THE FOSSIL EEPTILIA 



OF THE 



LIASSIC FORMATIONS. 



Order— SAUIIOPTERYGIA, Owen. 

 Genus — F l e s i os a u r u s , Con ybeare. 

 Species — Plesiosaurus dolichodeirus, Conybeare . 

 (Tabs. I — IV.) 



Of the Plesiosaurus dolichodeirus, Conyb., the first described and the typical 

 species of the genus, three more or less entire specimens have come under my obser- 

 vation, which have been obtained from the Lower Lias of Lyme Regis and Charmouth, 

 Dorsetshire. One of these, formerly in the possession of the late Duke of Buckingham 

 and now in the British Museum, was the subject of Conybeare's original description.* 

 A second, in the British Museum, is figured by Buckland in his ' Bridgewater Treatise/ 

 vol. ii, pi. xix, fig. 2 ; the third, also in the British Museum, is the one which I have 

 selected for illustration in the present Monograph (Tabs. I and II). In this the 

 vertebral series is entire ; there is no break in the long cervical region, as in the other 

 two specimens ; its perfection, in this respect, satisfactorily shows that the head is at, 

 or nearly at, the correct distance from the trunk, with the neck outstretched, in the 

 two former specimens, the greater completeness of which, in regard to the limbs, 

 supplies what is wanting in this respect in the present skeleton (see Tab. I, figs. 2 

 and 3). 



The condition of the vertebral column in the originally described or type-specimen 

 of the Plesiosaurus dolichodeirus is such as to suggest that the carcass, after it sank to 



DO ' 



* 'Transactions of the Geological Society,' 2nd series, vol. i, p. 381, pi. xlviii. 



1 



