Professor Owen on British Fossil Reptiles. 77 



monitors of the Thuringian Zechstein are older than the la- 

 byrinthodonts of the Keuper ; and among British reptiles, the 

 thecodont lizards of the magnesian conglomerate have equal 

 claims to a more ancient origin. 



The questions, which the unbiased collector of evidence 

 bearing upon the fixity or mutability of species has next to 

 resolve respecting these primeval lizards, are, whether they 

 appeared under the form of the low organized species, which 

 one naturalist classes with Sauria, another with Ophidia, or 

 whether they exhibit indications of having emerged, by pro- 

 gi-essive development of structure, from any lower organized 

 pre-existing group of cold-blooded animals? To these inquiries 

 the palaeontologist must reply, that the thecodont lizards of 

 the zechstein and magnesian conglomerates combine well or- 

 ganized extremities, with teeth implanted in distinct sockets, 

 instead of being soldered, as in frogs, to a simple alveolar pa- 

 rapet ; and that, therefore, if they existed at the present day, 

 they would take rank at the head of the Lacertian order, and 

 not among the families most nearly allied to the inferior rep- 

 tiles. Neither are the modifications of the skeleton of the 

 Rhynchosaur, from the new red sandstone, such as indicated 

 that singular lacertian to have been derived from the Ophidi- 

 an or Batrachian orders ; but, on the contrary, they connect 

 it more closely than any known recent species with Chelonia 

 and birds. 



The nearest approximation to the organization of fishes is 

 made by the ichthyosaurus, an extinct genus, which appears 

 to have been introduced into the ancient seas, subsequent to 

 the deposition of the strata inclosing the remains of the theco- 

 dont lizards. The ichthyic characters of this genus of marine 

 saurians are not of a very important kind, being limited, like* 

 the modifications of the mammalian type in whales, to a rela- 

 tionship with locomotion in water, while all the modifications 

 of the skeleton which are connected with the respiratory, di- 

 gestive, or generative functions, are conformable with the 

 highest or saurian type of reptiles ; such as the cranial ana- 

 tomy, the large size of the intermaxillary bones excepted ; the 

 dental structure, which corresponds with that of the posterior 

 teeth in alligators ; the articiUation of the neurapophyses to 



