180 BRITISH FOSSIL REPTILES. 



The carapace (Plate 53) includes tlie nuchal plate (c^) ; the eight neural plates 

 (« 1— s 8) which are connate with the neural spines of the vertebras of the carapace ; 

 and the corresponding eight ^^airs of costal plates, except the eighth on the right 

 side (pis. 1— s). The hindmost neural plates, and all the marginal plates, save the 

 first of the left side connected with the nuchal plate, are wanting. 



The length of the carapace, from the anterior margin of the nuchal plate to the 

 posterior one of the eighth neural plate, is 13 inches ; the breadth of the carapace, 

 across the third costal plates, is 11 inches. The outer surface of the carapace is 

 very slightly convex. 



The nuchal plate (c/*) is six-sided ; the anterior and antero-lateral borders are 

 of equal length, and are the longest of the six; the hind border is the shortest: 

 the latter is angularly notched for the reception of the first neural plate (s l). 

 The front border is slightly convex, with a feeble median concavity. The greatest 

 breadth of the nuchal plate, which is across the angles between the antero-lateral 

 and postero-lateral borders, is 3 inches -i lines ; the length of the nuchal plate is 2 

 inches 3 lines. The outer surface of the nuchal plate is impressed by a triradiate 

 groove, indicative of the junction of the two nuchal scutes with each other and 

 with the first vertebral scute {v l). The portion of the median series of bony 

 plates answering to the first neural plate in ordinary Chelonia is divided by a 

 transverse suture into two plates, — a circumstance which corroborates the 

 homology of the neural plates with the median dermal bones of the Crocodilia, 

 and opposes their interpretation as the vertebral spinous processes unwontedly 

 expanded. The indented boundary between the first (v l) and second (v 2) 

 vertebral scutes crosses the first neural plate (« i) immediately in advance of the 

 dividing suture in question. 



The second {s 2) to the eighth (s g) neural plates inclusive are six-sided, with 

 the antero-lateral sides or borders the shortest, and the postero-lateral ones the 

 longest; the third, fifth, and eighth are crossed by the boundary impressions 

 between the vertebral scutes. They progressively diminish in length to the 

 seventh ; the eighth resuming the normal length, unless the indentation between 

 the fourth (v 4) and fifth (y 5) vertebral scutes conceal, as I suspect, a suture 

 dividing the plate (s s). 



The first pair of costal plates (pi. 1) is impressed by the boundary lines 

 dividing the second marginal scutes, the first vertebral scute (« 1), the second 

 vertebral scute {v 2), and the first costal scute (c l) ; it unites with the nuchal (ck) 

 and first and second marginal plates, with both divisions of the first neural plate 

 (s 1) with the anterior truncated angle of the second neural plate (« 2), and with 

 the second costal plate (pi. 2) ; the second (pi. 2) to the seventh (pi. 7) costal plates 

 have the posterior angle of their mesial extremity truncated ; they become slightly 

 expanded at their lateral extremity ; and, after the third, they gradually decrease 



