272 R. Lydeliker and G. A. Boulenger — Notes on Chelonia. 



Cope^ that the plastron of Pleurosternum has no intergular shield,'* 

 and the genus is accordingly referred by him to the Cryptodira ; 

 whereas its true position, as was pointed out by Prof. Eiitimeyer, is 

 with the Pleurodira ; and with that group — the Pelomedusidce and 

 Peltocephalidce of Gray — characterized by the presence of eleven, 

 instead, of nine, plastral bones. 



With regard to the carapace figured by Sir E. Owen in pi. iv. of 

 his " Wealden and Purbeck Eeptilia," under the name of Pleuro- 

 sternum emargmatum (of which it is the type), it appears from the 

 emargination of the anterior border that the specimen does not 

 belong to that genus at all ; and it is highly probable that it should 

 be referred to Plesioclielys, although, as only the ventral aspect of 

 the carapace is visible, this cannot be definitely determined ; the other 

 specimen figured by Sir E. Owen under the same name cannot 

 apparently be distinguished from Pleurosternum Bulloclci. Another 

 carapace from the Purbeck has been figured by Sir E. Owen in pi. i. 

 of the above-mentioned work under the name of Pleurosternum 

 latiscutatum, which difi'ers from P. BidlocTci by the notch in its 

 anterior border, in the presence of a nuchal epidermal shield, and 

 in the narrowness and length of the neural (vertebral) bones. A 

 specimen of both carapace and plastron in the Museum (No. 23624) 

 from the Wealden, which is evidently specifically identical, shows 

 that there was no mesoplastron, and the species may apparently 

 therefore be referred to the genus Plesioclielys.^ A second English 

 species of that genus is indicated by an imperfect shell from the 

 Wealden in the collection of the Museum (No. 28967) which 

 evidently belongs to the group containing the Upper Jurassic P. 

 Soluthurnensis and P. Sanctce- Verence of Eiitimeyer,* and agrees so 

 closely with the latter that it may apparently be referred to the same 

 species; a younger shell of the species (No. E. 583) from the 

 Wealden near Hastings is also contained in the collection. Two 

 plastra from the Purbeck (No. 45937) have a large central vacuity, 

 and thereby agree with P. Etalloni, Eiitimeyer.^ Prof. Eiitimeyer^ 

 has already observed that the fragmentary remains from the Wealden 

 figured by Sir E, Owen' under the name o^ Platemys and Chelone 

 costata do not belong to those genera, and he has suggested that they 

 may be Thallasemydiaus, but there seems no reason why they should 

 not be referred to that group of Plesioclielys in which there is a large 

 plastral vacuity. The occurrence in the English Wealden and 

 Purbeck of several species of Plesiochelys apparently closely allied 

 to those of the Upper Jurassic of the Continent is a matter of con- 

 siderable interest. 



1 Proc. Amer. PhH. Soc. 1882, p. 143. 



2 The presence of an intergular shield is distinctly mentioned on page 5 of Owen's 

 " Wealden and Purbeck Eeptilia," although it is not sliown in a complete state in 

 any of the figured specimens. 



^ Mr. Boulenger takes this view. — [R. L.] 



* Neue Denks. schweiz. Ges. Nat. vol. xxv. pis. xii. xiii. 



s Ibid. pi. xi. 



6 Verh. Nat. Ges. Basel, op. cit. p. 166. 



7 "Wealden and Purbeck Eeptilia, pis. viii. and ix. 



