426 BRITISH FOSSIL REPTILES. 



Tipper surface. The neural arch is provided witli anterior and posterior oblique 

 processes, and a broad and thin spine developed at its posterior part, and strongly 

 inclined backwards at its origin; lastly, the vertebra has a large medullary cavity 

 in the centre of the body, filled, in the fossil, with spar. In all these particulars the 

 Palseontologist acquainted with the excellent description by M. Eudes-Deslong- 

 champs of the roikilopleuron Bucklandi* from the Oolite at Caen, will not fail to 

 recognise the distinctive characters of that species in the present fossil. It is 

 attached to a mass of the common Wealden stone which is quarried at Tilgate, and 

 was associated with the bones of the Iguanodon. 



The length of the present vertebra is 3 inches 9 lines, or 9^ centimeters; that 

 of the caudal vertebrae of the Poikilopleuron of Caen is about a decimeter.f We 

 may conclude, therefore, that the individual from the Caen Oolite and that from 

 the Wealden were of the same si^e, and, from this correspondence, it is most likely 

 that the size — 25 French feet, which M. Deslongchamps assigns to the entire animal 

 — is the common size of the species. 



From the size and position of the transverse process, the Tilgate vertebra corre- 

 sponds with the second or third of the first series of caudal vertebrae of the Caen 

 Poikiloplcuroti figured by M. Deslongchamps. There is one character in the Wealden 

 vertebra which is not mentioned in M. Deslongchamps' description of the Caen 

 species, viz. a longitudinal sulcus at the middle of the under surface of the body of 

 the vertebra, at least, at its anterior half; the sulcus is not deep, and is 1 centimeter 

 or 4 lines in breadth. The fortunate fracture which demonstrates the peculiarly 

 large medullary cavity in the centre of the vertebral body gives the best proof that 

 could be required of the generic identity of the Wealden vertebra with the Caen 

 Poililojjlcuron ; and the absence of that cavity in the vertebrae of Megalosaurus, which 

 I have determined by a section of one of the caudal vertebrae, establishes the distinc- 

 tion between that genus and Poikilopleuron. 



In the form of its sub-biconcave vertebrae, and the simplicity of their neural 

 arch as compared with the Streptospondylus and the Dinosaurians, the Poikilopleuron 

 manifests its closer affinity to the amphicoelian Crocodiles. It agrees with the 

 Teleosaurns in the comparative shortness of the fore legs ; the mode of articulation 

 of the vertebral ribs a])pears to be the same, and there is no evidence that it differs 

 ill the structure of the abdominal ribs. 



The number of caudal vertebrae would appear to be greater; but I know not in 

 what material respect the Poikilopleuron resembles the Lizard tribe more closely 

 than does the Teleosaurus, unless it should be proved to have five toes on the hind 

 foot, and to want the dermal armour. Subsequent discoveries may prove it to 

 belong, like the Megalosaurus, to tiie Dinosaurian order; but as the Poikilojjleuron is 



* ' Menioires de la Societe Linn, de Normandie,' 4to, 1836. 



f "Nos verlebres out chacune environ un decimetre de long." — Deslongchamps, loc. eit., p. 53. 



