LIASSIC PLESIOSAURS. 



3 



right side are in an instructive state of preservation, especially those of the hind fin, 

 which exemplifies the slight superiority of length as compared with the fore fin, cha- 

 racteristic of the present species. 



The following are admeasurements of corresponding parts of the three skeletons 

 above mentioned, that of " entire length" being now capable of being given by reason 

 of the integrity of the cervical region of the spine between the head and the pectoral 

 or scapulo-coracoid arch. 



From the amount of concordance in the dimensions of the above three skeletons, it 

 may be inferred that the average length of the mature animal of the present species of 

 Plesiosaurus was between nine and ten feet. Two specimens of certain portions of the 

 skeleton, now in the British Museum, one of which is the subject of Tab. Ill, support 

 this conclusion. 



Vertebral characters (Tabs. Ill and IV). 



Cervical series. — The cervical vertebrae of the Plesiosaurus dolichodeirus, at the fore 

 part of the neck (Tab. Ill, fig. 1, a, c4— 7), have the centrum (c) of a length equalling 

 the breadth of the articular end ; but the dimension of breadth increases in a greater 



* Estimated at that of the lower jaw. 



■\ Nine inches, if the angle of the jaw he restored, as dotted in Tab. IL 



X It may be that the head has been drawn a little forward in the displacement of the anterior cervical 

 vertebrae. 



§ Some of the terminal phalanges are here estimated for. 



