18 FOSSIL REPTILIA OF THE LONDON CLAY. 



tenth neural plate ; and the tooth-like continuation of the rib from the posterior angle 

 of the eighth costal plate {pls, T. IV, fig. 2). These portions of the carapace, 

 from their smooth surface, the impressions of the horny scutes, the form of the 

 vertebra] ends, and the concavity of the upper surface of the costal plates, evidently 

 belong to the same species as the fossil last described. 



A similar mass of Sheppey clay-stone, in Mr. Lowe's collection, supports a larger 

 proportion of the hinder part of the carapace, including the sixth, seventh, eighth, 

 ninth, and tenth neural plates, part of the fifth neural plate, more or less of the last 

 four pairs of costal plates, with the impressions of the third and fourth ribs of the 

 right side ; the impression of apparently the whole of the free, slender, termination of 

 the third rib is preserved, and also that of the fifth rib, confirming the generic 

 characters indicated by the skull. The smooth outer surface of the bones of the 

 carapace, the forms of the neural plates, and the concomitant modification of the 

 commencement of the costal plates articulated therewith, concur to establish the 

 specific distinction from the Chelone hreviceps, and indicate the specimen to belong to 

 the present species, Chelone longiceps. The seventh, eighth, and ninth neural plates 

 progressively decrease in size ; and the ninth presents a simple, quadrangular, oblong 

 form ; the tenth neural plate suddenly expands, and has apparently a triangular form, 

 but its posterior border is incomplete. 



The indications of the comparative flatness of the carapace of the Chelone longiceps, 

 (in this respect, as in the elongated and pointed form of the skull, approaching the 

 genus Trionyx^ which were derived from an examination of the foregoing fragments, 

 and particularly of the portion preserved with the cranium on which the species is 

 founded, are fully confirmed by the almost entire carapace which, subsequently to the 

 publication of my ' Report on British Fossil Reptiles,' where the present species is 

 first noticed, I have had the opportunity of examining in the collection of Mr. 

 Bowerbank. 



This carapace, as compared with that of the Chelone hreviceps in the same collection, 

 presents the following differences : — it is much broader and flatter. The neural plates 

 are relatively broader ; the lateral angle from which the intercostal suture is continued, 

 is much nearer the anterior margin of the plate — the Chelone longiceps, in this respect, 

 resembling the existing species of turtle (see fig. 1, p. 3). The costal plates are 

 relatively longer ; they are slightly concave transversely to their axis on their upper 

 surface, while in Chel. hreviceps they are flat. The external surface of the whole 

 carapace is smoother ; and although it is as depressed as in most turtles, it is more 

 regularly convex ; not sloping away by two nearly plane surfaces from the median 

 longitudinal ridge of the carapace. 



The following minor differences may be noticed in the two Sheppey Chelonites : 

 the nuchal plate of the Chel. longiceps (Tab. V, fig. 1, ch) is more convex at its 

 middle part, and sends backwards a short emarginate process to join the first neural 



