CRETACEOUS EORMATIONS. 27 



animal, that which the vertebral joint freely allowed in the dead carcase before it 

 became fixed in the chalk-mud. 



Assuming that the specimens fig. 1 and fig. 4, T. X, give the natural length 

 of the neck and trunk of the Bolichosaurus, to which trunk the size of the anterior 

 caudal vertebrse indicate a long and strong tail to have been appended, the progress 

 of the long and slender Bolichosaurus through the water would be by flexuous and 

 undulatory lateral movements of the entire body, like those of a water-snake or eel. 



The specimen fig. 1, T. X, demonstrates that this procoelian Lizard of the cretaceous 

 period had a smaller head and a longer, more slender and tapering neck than any 

 known existing species of the Lacertian order of Reptiles. 



The hinder moiety of the trunk-vertebrae, with part of the pelvis and root of the tail, 

 fig. 4, — which, from the correspondence of size, shape and structure of the vertebrse, 

 I refer to the Bolichosaurus, and from the evidence above given, corroborated by the 

 disposition of the parts in the chalk-matrix, I believe to be part of the same skeleton 

 as the anterior moiety, fig. 1, T. X — includes twenty-one abdominal, two sacral, and 

 five caudal vertebrse. They have been exposed by the removal of the chalk from 

 their inferior or ventral surfaces, the operation having been commenced from the oppo- 

 site side of the block from that at which the exposure of the part of the skeleton in 

 the other portion of the same block of chalk has been efi'ected. The bodies of the 

 vertebrse and the ribs show the same disposition and slight degree of dislocation as in 

 the specimen. The ribs have been pressed by the weight of the surrounding chalk, as 

 the soft parts yielded and became decomposed, close to the sides of the vertebrae, but 

 with scarcely any further dislocation ; and the vertebrse, maintaining the close articu- 

 lations of their cup-and-ball surfaces, continue, with not more deviation from the 

 straight line than a slight flexuosity, like that shown by the last six vertebrse in the 

 moiety of the skeleton in T. X, fig. 1. 



The under surfaces of the vertebrse exhibit the same smooth, imperforate, longitu- 

 dinally concave, transversely convex surfaces, as in the anterior dorsals of the last- 

 described specimen : as in that specimen, also, they are longer in proportion to their 

 breadth than in the Monitor {Varanus ?) figured by Cuvier,* or than in the Iguana, 

 Cyclodus and Tiliqua .- the diapophyses rise by a shorter base than in the Iguana: in an 

 Australian Tiliqua I find the under surface of the centrum with two vascular perforations 

 towards its fore part, which are not present in the Bolichosaurus, nor in many of the 

 existing Lacertians. Each diapophysis forms a short rounded tubercle, immediately 

 below the base of the anterior zygapophysis ; and the simple, slightly expanded head 

 of the rib is excavated to fit the tubercle. In the degree of compression and expan- 

 sion of the proximal portions of the ribs, and in their curvature, the present precisely 

 corresponds with the preceding portion of the skeleton of the Bolichosaurus ; and it is 



* Ossem. Foss., v, pt. ii, pi. 17, fig. 23. 



