228 Mr. H. G. Seeley on Chelonian Remains 



curious, the characters drawn in Prof. Owen's figure (pi. x.) 

 being repeated in the main in this specimen. The eighth pair 

 of costal plates bear a small tenth pair of ribs*, supposing the 

 first costal to have had the usual short pair in front of the 

 proper rib of the plate. Behind these ribs and the neural 

 plate marked by Prof. Owen as the ninth (which appears to 

 me to be as wide as the preceding one), lies a diamond-shaped 

 terminal part of the carapace. A transverse suture appears to 

 divide it into two nearly equal parts — one anterior, the other 

 posterior. The anterior part shows throughout its length two 

 subparallel longitudinal sutures, which separate a middle part, 

 the neural plate, from what would be a ninth pair of costal 

 plates, though they do not support the ninth pair of ribs. 



The posterior half of the diamond shows a transverse suture 

 which separates a narrow anterior piece from the larger poste- 

 rior trapezoidal plate. If the preceding plates were rightly 

 numbered, these plates would be the eleventh and twelfth 

 neural. 



The characters described are, in their essential points, re- 

 peated in another carapace, figured by Prof. Owen in pi. x. Af, 

 where the ninth pair of ribs are represented as being prolonged 

 to the marginal plates. That lithograph shows the neural 

 plates to extend far in front of their corresponding costal 

 plates, herein being unlike Chelone. It also shows that the 

 neural plates which Prof. Owen has numbered, in plate x., 

 5, 6, 7, 8, 9, 10, respectively, should be numbered 4, 5, 6, 7, 8, 

 while the plates beyond should be numbered 10 and 11 ; thus 

 in number the neural plates conform to the Chelonian type, 

 though their arrangement is unlike that in any of the recent 

 genera. 



In the typical specimen figured, and in this specimen also, 

 the marginal plates are remarkable for their narrowness ; for 

 though of some width from below upward, they seem to be 

 only from an eighth to a quarter of an inch thick ; and the 

 specimen now described shows no trace of the ribs being in- 

 serted into holes. The pygal plate, presuming such a plate 

 to have existed, must have been of the same thin character as 

 the others. There is no trace of sutures between the marginal 

 plates. 



* " Perhaps no monstrosity would sooner arrest the attention, or excite 

 more wonder in the comparative anatomist, than the appearance in a 

 recent or fossil chelonian of a greater number of pairs of ribs in the cara- 

 pace than 8 " (Owen, Palseont. 1851). Yet that condition had already 

 been figured by Prof. Owen (Palaeont. 1849, t. x. & x. a) without arousing 

 the anticipated emotion. t Since perished. 



