H. Lydekker and G. A. Boiilenger — Notes on Chelonia. 271 



preoccupied ; and Prof. Cope had previously applied the geueric 

 term Fuppigerus to several of Owen's species ; some of which may, 

 however, belong to other North American genera.^ At least one 

 of the carapaces of the Cheloniaus from the London Clay has 

 nine costal bones, which is a character of Cope's Propleuridce." This 

 group does not, however, form the proper subject of the present 

 communication.^ 



Purbeck and Wealden. — The first genus for consideration is 

 Pleurosternum, in which there appears a considerable amount of 

 confusion. In their 'Monograph of the Chelonian Eeptilia of the 

 London Clay' (Pal. Soc, 1849) Owen and Bell figured in pi. xxi. a 

 Chelonian plastron nnder the name of Platemys BidlocM, the specific 

 name * dating from 1842. This specimen, now in the British 

 Museum, is characterized by the presence of a mesoplastral bone, 

 and also by an intergular epidermal shield. Owing to the former 

 feature Prof. Eiitimeyer^ pointed out that the specimen could not 

 have belonged to Platemys, but must be referred to the genus 

 Pleurosternum of the Purbeck ; he was, however, necessarily unaware 

 that the specimen is really from the Purbeck, and not from the 

 London Clay as stated by Owen and Bell. A comparison of this 

 plastron with other Purbeck examples of Pleurosternum shows that 

 it cannot be distinguished from the form figured by Owen in his 

 Purbeck and Wealden Eeptilia (Mon. Pal. Soc. 1853) under the 

 name of Pleurosternum ovatum, with which the specimen figured in 

 pi. vii. under the name of P. emarginatum appears also specifically 

 identical ; under these circumstances the name Pleurosternum Bulloclci, 

 as being the earliest, must be adopted for the common Purbeck 

 form." It should further be observed that it has been stated by Prof. 



1 See Amer. Nat. vol. xx. p. 968 (1886). 



2 Cope {loc. cit.) states that his Propleuridm is identical with Dollo's FachyrJiyn- 

 ehid(e. The type species of the latter is, however, expressly stated to have only 

 eight costals, which Cope makes a character of Fuppigerus. 



2 It is usual among English writers to term the bony parts of the Chelonian shell 

 "plates," andthehorny epidermal covering " scutes " ; but Prof. Huxley, "Anatomy 

 of Vertebrated Animals," 1st edition, pp. 197, 200 (1871), uses the former term for 

 both. Siuce, however, the term "scute" is applied to the dermal bones of the 

 Crocodilia and of the ArmadUlos [vide Huxley, op. cit. pp. 250, 338), which are 

 homologous with some of the bony elements of the Chelonian shell, this use is cer- 

 tainly objectionable ; and in previous works I have reversed the application of the 

 two terms. This application is not, however, thought advisable by Mr. Boulenger, 

 who usually employs the terms in their older sense ; as a compromise, in the present 

 paper the bony elements will therefore be alluded to as " bones," and the elements of 

 the epidermal layer as " shields." — [E. L.] 



* Eep. Brit. Assoc, for 1841, p. 164 (1842). 



5 Verb. Nat. Ges. Basel, vol. vi. p. 121 (1873). 



" Specimens of Purbeck Chelonia in the Cambridge Museum have been referred by 

 Prof. Seeley (Index to Aves, Ornithosauria, etc., in the Cambridge Museum, pp. 86, 

 87 [1869] ) to Pleurosternum, under the names of P. Sedgwicki, P. Vansittarti, P. 

 Oweni, and P. typocardium. These specimens have, however, not been figured, and 

 cannot therefore be compared with those in the British Museum ; some of them may 

 perhaps belong to Plesiochelys, while the distinction of others from P. Bullocki is not 

 clear. 



