179 



border occupied by the latter is convex, and exhibits three deep sinuosities — 

 the middle one and the one on each side, as seen in Fig. 1, Plate IX. 



Eight pairs of costal plates succeed the nuchal plate. The second, fifth, 

 and sixth pairs expand considerably outward, more especially the last of 

 these. The others are of more uniform breadth. 



The specimen possesses only six vertebral plates. Of these, the first is the 

 longest and widest. Its fore border is convex, and nearly in a line with the 

 suture between the nuchal and first pair of costal plates. The lateral borders 

 diverge to the back angles, which are truncated to join the second pair of 

 costal plates. 



The second and third vertebral plates are nearly equal in size, and are 

 reversed coffin-shaped. The fourth plate is smaller, and oblong quadrate, 

 with convex borders. The fifth plate is obverse coffin-shaped, shorter, but 

 wider than the former. The sixth vertebral plate has not more than half its 

 usual development. It is pentagonal shield-like, and is included between the 

 angles of the fifth and sixth costal plates. 



The posterior half of the sixth costal plates, and those succeeding them, 

 unite in the median line by a tortuous suture. 



The surface of the carapace presents a nearly uniform reticular aspect 

 and the thickness of the bones is of the usual proportion. 



The measurements of the specimen are as follows : 



Space occupied by the six vertebral plates 



Breadth of nuchal plate • 



Extent of nuchal plate in median line 



Breadth together of seventh pair of costal plates 

 Breadth together of eighth pair of costal plates . 



Inches. 



10£ 



First vertebral plate . . 

 Second vertebral plate 

 Third vertebral plate . 

 Fourth vertebral plate 

 Fifth vertebral plate . . 

 Sixth vertebral plate . . 



