EXPLANATION OF PLATE 11. 23 



Plate 11. V. I. p. 138. 



1. Side View of the head of an Ichthyosaurus, marking 



by corresponding letters, the analogies to Cuvier's 

 figures of the same bones in the head of the Croco- 

 dile. (Conybeare.) 



2. Posterior part of a lower jaw of Ichthyosaurus com- 



munis, in the Oxford Museum. (Conybeare.) 

 3 — 7. Sections presented by the component bones of Fig. 



2 in fractured parts above each section. (Conybeare.) 

 8. View of the lower Jaw of Ichthyosaurus seen from 



codiles ; but as the horny scales of Fishes, and dermal bones of Cro- 

 codilean animals* are preserved in the same Lias with the bones of 

 Ichthyosauri, we may infer that if the latter animals had been furnish- 

 ed with any similar appendages, these would also have been preserved, 

 and long ere this discovered, among the numerous remains that have 

 been so assiduously collected from the Lias. They would certainly 

 have been found in the case of the individual now before us, in which 

 even the Epidermis, and vessels of the Rete Mucosum have escaped 

 destruction. 



Similar black patches of petritied skin are not unfrequently found 

 attached to the skeletons of Ichthyosauri from Lyme Regis, but no re- 

 mains from any other soft parts of the body have yet been noticed. 



The preservation of the skin shows that a short interval only elapsed 

 between the death of the animal, and its interment in the muddy sedi- 

 ment of which the Lias is composed. 



Among living reptiles, the Betrachians afford an example of an 

 order in which the skin is naked, having neither scales nor dermal 

 bones. 



In the case of Lizards and Crocodiles, the scaly, or bony coverings 

 protect the skin from injury by friction against the hard substances 

 with which they are liable to come into contact upon the land ; but to 

 the Ichthyosauri which lived exclusively in the sea, there would seem 

 to have been no more need of the protection of scales or dermal bones, 

 than to the naked skin of the Cetacea. 



In the case of Plesiosauri also, the non-discovery of the remains 

 of any dermal appendages with the perfect skeletons of animals of 

 that genus, leads to a similar inference, that they too had a naked 

 skin. The same negative argument applies to the flying Reptile 

 Family of Pterodactyles. 



