CRETACEOUS FORMATIONS. 19 



to light the modifications of the head and limbs of the Protemys : from those of the 

 plastron we may infer that the species was more aquatic in its habits than the 

 typical Emydians. The Protemys serrata may have been an Estuary species, and its 

 discovery in the same formation and quarry as that in which the remains of an 

 Iguanodon have been found, adds probability to the explanation of the occurrence of 

 the latter in a Green-sand or Neocomian Deposit, on the supposition that the carcase 

 had been drifted out to sea. 



Okvkk—LACERTILIA. 



In passing from the Tertiary to the Secondary periods of Geology, in quest of the 

 evidences of Reptilian organisation, we have found no material change in that of the 

 Chelonian order ; the characters by which the marine species are now generically 

 separated from other Tsstudines of Linnaeus, and which were not deemed worthy 

 of that distinction by the great systematic reformer of Natural History, are recog- 

 nisably retained in the old Turtles, the contemporaries of the Ichthyosaurs, Plesiosaurs, 

 Pterodactyles, and Belemnites, that swam the ocean in which the Corals and Sponges 

 lived, which deposited the main part of the material that now constitutes our Chalk 

 Downs. The differences which are traceable on a comparison of the Turtles of that 

 period with those of the Tertiary deposits and of the actual seas, merely prove them 

 to have been distinct species, with some slight indications of a nearer affinity to the 

 Emydian type of structure than we observe in the present representatives of the genus 

 Chelone. 



The Lizards of the present day are characterised, with the exception of one genus, 

 Gecko, by the same cup-and-ball articulation of the vertebras as the modern Crocodiles, 

 viz. with the cup at the fore part of the body of the vertebra and the ball at the back 

 part, an arrangement signified by the term " proccelian," as applied to such vertebrae. 

 The fossil Lizards of the Cretaceous period, whether terrestrial, amphibious, or more 

 especially modified for marine life, present the same proccelian type. 



Tribe, Repentia. 

 Genus, Raphiosaurus, Owen. 



'Transactions of the Geological Society,' vol. vi, 2d Series, p. 413, April, 1840. 



Species, Raphiosaurus suhdidens, Owen, (Tab. X, figs. 5 and 6). 

 Report on British Fossil Reptiles, 'Trans, of British Association,' 1841, pp. 145, 190. 



In a Memoir communicated to the Geological Society of London in 1840, and in 



