84 REPORT — 1841. 



POIKILOPLEURON BUCKLANDI, Eudes-Deslongehamps. 



Nos. 1^ and — , in the Mantellian Collection, are the two moieties of a 

 fossil caudal vertebra, fractured obliquely across the middle of the body, the 

 lensth of which is to the breadth of its articular extremity as 3 to 2 : both 

 extremities are slightly concave ; the body is gradually contracted from the 

 two extremities towards the middle part ; bears a transverse process deve- 

 loped from the posterior and upper part of its side, behind which there is a 

 shallow groove ; has the neural arch anchylosed, without trace of suture, to 

 nearly the whole of the longitudinal extent of its upper surface. The neural 

 arch is provided with anterior and posterior oblique processes, and a broad 

 and thin spine developed at its posterior part, and strongly inclined back- 

 wards at its origin ; lastly, the vertebra has a large meduUaiy cavity in the 

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

 the Palaeontologist acquainted with the excellent description by M. Eudes- 

 Deslongchamps of the Poikilopleuron 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 Ignanodon. 



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 deci- 

 meter*. We may conclude, therefore, that the individual from the Caen 

 oolite and that from the Wealden were of the same size, and, from this cor- 

 respondence, it is most likely that the size — 25 French feet, which M. Des- 

 longchamps assigns to the entire animal — is the common size of the species. 



The vertical diameter of the articular end of the body of the Wealden ver- 

 tebra is 2 inches 3 lines (5J centimeters) ; the transverse diameter of the 

 same part is 2 inches 2 lines (5^ centimeters) ; the transverse diameter of 

 the middle contracted part of the body is 1 inch 4 lines (S-j centimeters). 

 The external free surface of the vertebra is almost smooth, being faintly 

 marked by fine striae. The form of the terminal surfaces of the centrum is 

 a full ellipse, with its long diameter vertical. The longitudinal sulcus at the 

 upper part of the side of the body is shallow, and slightly bent, with the con- 

 vexity downwards ; the base of the transverse process is continued from the 

 upper boundary of the groove, and extends along the posterior half of the 

 upper and lateral part of the centrum, and upon the base of the neural arch, 

 whicli is here wider than the centrum : the transverse process is broken off 

 near its origin. The base of the neurapophysis or side of the neural arch 

 leaves only a very small portion of the upper part of the centrum free at its 

 anterior and posterior part, to form the hole for the transmission of the spinal 

 nerve : the distinction between the present genus and the Cetiosaurus is 

 well marked in this respect. The neurapophyses have a less vertical extent 

 than in the corresponding vertebra of the Cetiosaurus, or even than in the 

 Crocodile. From the upper part of the centrum to the upper edge of the 

 anterior oblique process in a vertical line is only 1 inch, or about 2^ centi- 

 meters. The base of the spinous process is not thickest at its posterior 

 margin, but gradually expands transversely as it extends forwards, and then, 

 at a distance of 10 lines from its posterior part, it quickly contracts to a very 

 thin plate, which is continued forwards to the conical depression at the inter- 

 space of the origin of the anterior oblique processes. The upper jiart of the 

 spine is broken away, but the remaining base has the same backward inclina- 

 tion as in the Caen Poikilopletiron. 



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



* " Nos vertebres ont chacune en^■iron un decimetre de long." — Deslongchamps, I. c, p. 53. 



