TR10NYCHIDJE. 17 



R. 1437. A left hyposternal. This specimen indicates an individual 

 slightly larger than No. 36810. Hastings Collection. 



Trionyx incrassatus, Owen l . 



Carapace much depressed, with the neurals below the level of the 

 adjacent portions of the costals, and the sculpture somewhat coarser 

 than in the preceding species, and tending to a pustular type in the 

 neural region. Nuchal slightly emarginate and not very convex, 

 with the lateral dentations of the unsculptured portion distinct, and 

 only a small moiety of this part in advance of the median emargina- 

 tion ; limits of sculptured portion not well-defined. No callosity 

 on the entoplastral. Centra of dorsal vertebraa elevated. 



The above description depends in part on the correctness of the 

 reference of the second of the undermentioned carapaces to this 

 species. 



Hah. Europe (England). 



R. 1433. The anterior portion of the carapace ; from the Upper 

 {Fig.) Eocene (Lower Oligocene) probably of Hordwell, Hamp- 

 shire 2 . This specimen may be taken as the type. 

 Described and figured by Owen in his ' Reptilia of the 

 London Clay, &c/ pt. i. p. 5, pi. xviii. It shows the nuchal 

 and two first neurals and the first three costals of either 

 side. The anterior angles of the first neural are truncated ; 

 the first costal narrows greatly towards its outer extremity, 

 and the outer margins of the costals are of moderate 

 thickness and bevelled. The inferior surface of the 

 nuchal, and the prominent centrum of the vertebra 

 underlying the first neural are very different from the 

 corresponding parts in T. henrici, No. 30413. 



Hastings Collection. Purchased, 1855. 



30408. The carapace, wanting the nuchal bone ; probably from 

 (Fig.) Hordwell. Described and figured by Owen, op. cit. p. 5, 

 pi. xvii. In this specimen the first costal is wider than 

 in the preceding example, and the outer borders of all 

 the costals are very thick and abruptly truncated ; the 

 latter features being given by Owen as diagnostic of the 

 species. The neurals are much depressed below the 

 costals. Hastings Collection. 



1 Reptilia of the London Clay, &c. (Mon. Pal. Soo.), vol. i. pt. i. p. 51 (1849). 



2 Owen states that this and the following specimens are from the Isle of 

 Wight ; but they are entered in the Museum Eegister as from Hordwell. 



PART III. C 



