WEALDEN CROCODILES. 423 



Vertebra of Poikilopleuron. ' Crocodilia,' Plates G, 19. 



In the Museum of the Royal College of Surgeons, London, is a portion of a 

 caudal vertebra (No 59 of the ' Fossil Reptilia,' PI. G, figs. 5, G), presented by me, 

 and obtained from the submerged Wealden beds at Brook Point, Isle of Wight.* 

 The terminal articular surface (fig. 5) is elliptical, with the long diameter vertical, and 

 is slightly concave ; the middle of the centrum is contracted ; the fractured surface 

 (fig. 6) exposes a medullary cavity, surrounded by large, cancellous vacuities, which 

 have become filled with siliceous spar and pyritic matter. There is a small depression 

 on each side near the base of the neural arch, which seems to lead, like a pneumatic 

 foramen, into the cavities of the bone. The thin, outer wall of this open, cancellous 

 structure consists of very compact bone. This vertebra agrees in shape and structure 

 with those of Poikilojjieuron. 



To the genus Poikilopleuron it is most probable that the specimen No. -irh: '" 

 the Mantellian Collection, British Museum, belongs, as it agrees in size, in texture 

 and especially in the character of the external surface, with the caudal vertebra 

 above described. As it consists of the annular part or neural arch only, the test of 

 the medullary cavity of the body cannot be applied. It belongs to one of the ante- 

 rior dorsal vertebrae, and is distinguished by well-marked and peculiar characters 

 from the corresponding vertebrse of the Iguanodon, Megalosaurus, IlylcEosaurus, 

 Getiosauriis, and Streptospondi/lus ; and in the chief of these differences it approxi- 

 mates to the sub-biconcave Crocodilian type of vertebrae. By the characters here 

 given of this fragment it may be compared with more perfect vertebrse from the 

 Oolite of Maladrerie, near Caen, in the event of the remainder of the vertebral 

 column of the Poikilopleuron ever falling into the hands of its original discoverer. 



The present fossil is imbedded in the ferruginous sand of the Tilgate strata; its 

 antero-posterior diameter, from the extremity of the anterior to that of the posterior 

 zygapophysis, is 5 inches 4 lines. 



The neurapophyses (PI. 19, figs. 1 and 2, d) instead of rising and expanding to 

 form a broad platform, as in the Dinosaurian vertebrse, support the spinous (fig. 4, e) 

 and transverse («') processes by a longitudinal plate not more than from 3 to 6 lines 

 in transverse thickness ; from each side of this plate a horizontal, flat, broad, lamelli- 

 form diapophysis (e), supported below by a subvertical, triangular plate, extends 

 outward and a little upward ; and a broad, thin, and moderately high spinous pro- 

 cess arises, in a peculiar manner, by two laminse, from the whole antero-posterior 

 extent of the ridge-like summit of the neural arch. The fossil is broken in two; a 

 portion of the centrum adheres to the anterior part of the neural arch, demonstrating 

 the anchylosis of the two parts without trace of suture. In this respect the fossil 



* ' Catalogue of Fossil Reptiles and Fishes,' 4to, Loudou, 1S54, p. 15 



2o 



