30 (JHELONURATEMMINCKII. 



plate; that of the fourth is most elevated; these prominences make on each side 

 a lateral tuberculated ridge, quite as high as the vertebral, so that the shell is 

 tricarinate. There are thirty-one marginal plates, of which the nuchal or inter- 

 mediate is short, subquadrangular, and very extensive in the transverse direction; 

 it is concave anteriorly, and slightly so at its lateral borders, with a prominence 

 on its superior posterior face; the first marginal is irregularly pentagonal, with 

 an elevated prominence at its outer and anterior part, at which begins the lateral 

 carina; the second is subtrigonal, with its base before and rounded, and its apex 

 truncated and turned backwards; the third and fourth are elongated quadrilateral, 

 with their anterior margins slightly convex; the fifth, sixth and seventh are also 

 quadrilateral, but are much more elongated and narrow; the eighth is quadri- 

 lateral and broad; the ninth subrhomboidal; the tenth, eleventh and twelfth are 

 also subrhomboidal, each with a strong projecting point backwards, which gives 

 the serrated and dentated appearance to the posterior margin of the shell. On 

 the sides of the shell, and between the lateral and marginal plates, are interposed 

 three supernumerary plates on each side. There seems, however, to be some 

 variety in their number, for Troost, whose accuracy no one doubts, observed in 

 his specimens four, whereas in the only specimen that I have ever seen there 

 were but three; the anterior large pentagonal with an acute angle above, passing 

 in between the lower margins of the first and second lateral plates, and straight 

 below, where it joins the fifth and slightly the sixth marginal plates; the second 

 supplementary marginal plate is regularly quadrilateral, and is interposed between 

 the second lateral and sixth marginal, touching also slightly the seventh; the 

 third of these plates is also quadrilateral, and situated between the second and 

 third lateral and seventh marginal plates. 



The sternum is narrow and cruciform in shape, and resembles that of the last 

 described animal, though there the wings descend a little from the sternum, while 

 here they pass off at a right angle. Troost says it is covered with plates, similar 

 in form and number to those found on the sternum of the Chelonura serpentina; 

 yet in the specimen that I saw the abdominal plates were subdivided, and it 



