10 



FOSSIL EEPTILIA OF THE 



though apparently narrowed from side to side is not broken ; the neural canal 

 (Tab. V, fig. 2, n) presents a vertical diameter of 11 lines, and a transverse diameter 

 of 7 lines. The costal depression (Tab. IV, fig. 11, pi) extends nearer to the 

 posterior than to the anterior surface of the centrum. The articular surfaces of 

 the centrum show the characteristic depth of the concavity, but with relatively 

 less thick obtuse borders, Tab. V, fig. 2. 

 The dimensions of this vertebra are : 



tn. 



lines 



1 



7 



2 







1 



11 



2 



3 



2 



3 



2 







1 



1 



1 



4 



Length of centrum ....... 



Height of ditto .;..... 



Breadth of hinder surface of ditto .... 



From base of neurapophysis to end of postzygapophysis 

 From end of pre- to that of postzygapophyses 

 Breadth of neural arch across prezygapophyses . 



„ „ „ „ „ postzygapophyses 



Antero-posterior extent of base of neural spine . 



The vertebra, Tab. V, figs. 3, 4, and 5, appears to have come from the middle 

 of the neck of an older and larger Plesiosaurus, and it displays, in a striking degree, 

 the characteristics of that part of the Plesiosaurus Bernardi. 



The depth of the concavity of the terminal surfaces of the centrum is almost 

 ichthyosaurian ; the breadth of the convex border of each cavity is extreme, and 

 is equally divided between the smoother articular surface continuous with that 

 of the concavity, and the surface roughened by fine concentric linear impressions, 

 forming the outer part of the border, and indicative of the strong circular liga- 

 ments which tied the vertebrae together. 



Anchylosis of both neur- and pleur-apophyses is here complete ; and the 

 missing parts of both vertebral elements have been broken off. The neurapo- 

 physial suture is, however, traceable ; and the characteristic distance between it 

 and the cervical rib is thus exemplified. The rising between the vascular depressions 

 on the under part of the centrum (fig. 4) is broader and less ridge-like than in 

 the more advanced vertebras of the neck. In this vertebra, in relation to its more 

 posterior position in the neck, the transverse diameter has increased upon the lon- 

 gitudinal one, as is shown in the following admeasurements : 



Length of centrum . 



Breadth of ditto, posterior surface 



In. lines. 



1 9 



2 6 



The riblet, at its fractured surface (fig. 5, pi), shows an antero-posterior 

 diameter of 10 lines, a vertical diameter of 5 lines. 



Valves of the fry, or young, of a species of Plicatula (?) adhere to this fossil, 

 to which they attached themselves at the period when the cretaceous beds, 



