200 REPORT — 1841. 



transmutations. Ichthyosaurus, Plesiosaurus and Teleosaurus are, however, 

 genera which appeared contemporaneously on the stage of vital existence : 

 one neither preceded nor came after the other. How the transmutation theory 

 is to be reconciled to these facts is not obvious ; nor to these other, viz. that 

 the Teleosaur ceases with the oolite, while the Ichthyosaur and Plesiosaur 

 continue to co-exist to the deposition of the chalk, and disappear together 

 alike unchanged ; the Ichthyosaur manifesting as little tendency to develop 

 itself into a Plesiosaur, as this to degrade itself into the more fish-like modift- 

 cation of the Enaliosaurian type. 



If it were urged that the Strejitospo7idylus, or Crocodile with ball-and- 

 socket vertebrae, of which the remains occur in later secondary strata, when 

 the Teleosaur had ceased to exist, might be a modification of the apparently 

 extinct amphiccelian Crocodile, in which the vertebrae had undergone a pro- 

 gressive development, analogous to that by which the biconcave joints of the 

 vertebrae of the Tadpole are actually converted into the ball-and-socket joints 

 of those of the mature Frog, the facts of both geology and anatomy again 

 oppose themselves to such an hypothesis : for the remains of the Strepto- 

 spondylus occur likewise in the Whitby lias, which is the earliest formation 

 characterized by remains of the Teleosaurus ; and the modifications of the 

 vertebral structure, by which the Streptospondylus differs from its ancient 

 contemporary, and which it retains unaltered throughout the whole series of 

 oolitic strata, is no approximation to the ball-and-socket structure of modern 

 Crocodiles which first appears in the Mosasaurus and the Eocene Crocodiles, 

 but is the very reverse. As reasonably* might we infer that the Teleosaur was 

 an intermediate form between the Streptaspondylus and modern Crocodiles, 

 and that the anterior ball had first subsided, and a sub-biconcave type of ver- 

 tebrae had been produced before the posterior ball, which characterizes the ver- 

 tebrae of recent Crocodiles, was finally developed. 



If the present species of animals had resulted from progressive develop- 

 ment and transmutation of former species, each class ought now to present 

 its typical characters under their highest recognized conditions of organiza- 

 tion : but the review of the characters of fossil Reptiles, taken in the present 

 Report, proves that this is not the case. 



No reptile now exists which combines a complicated and thecodont den- 

 tition with limbs so proportionally large and strong, having such well-de- 

 veloped marrow bones, and sustaining the weight of the trunk by synchon- 

 drosis or anchylosis to so long and complicated a sacrum, as in the order 

 Dinosauria. 



The Megalosaurs and Iguanodons, rejoicing in these undeniably most per- 

 fect modifications of the Reptilian type, attained the greatest bulk, and must 

 have played the most conspicuous parts, in their respective characters as de- 

 vourers of animals and feeders upon vegetables, that this earth has ever wit- 

 nessed in oviparous and cold-blooded creatures. They were as superior in 

 organization and in bulk to the Crocodiles that preceded them as to those 

 which came after them. 



There is not the slightest ground for affirming that the proccelian Gavial of 

 the present day is in any respect more highly organized than the opisthocoe- 

 lian Gavial of the oldest lias. If the differences of vertebral structure in these 

 Crocodilians were contrasted, in reference to their relative approximation to 

 the vertebral structure of the higher animals, the resemblance of the ball-and- 

 socket joints of the spine of the Streptospondylus to those of certain mam- 

 mals would give precedence in organic perfection to the primasval Gavial. 



If, therefore, the extinct species, in which the Reptilian organization cul- 

 minated, were on the march of development to a higher type, the Megalo- 



