PLETTROSTEKtflD^. 207 



The genus Digerrhum was founded on the erroneous supposition 

 that the intergular shield is absent in Pleurosternum (as typified by 

 P. concinnum) ; the former genus was referred by its founder to the 

 Sternothceridce = Pelomedusidce } while the latter was made the type 

 of a family of Cryptodira \ 



The names Pleurosternum sedgwicki, P. vanslttardi, P. oivetii, atid 

 P. typocardium have been applied by Seeley 2 to specimens from the 

 Purbeck preserved in the Woodwardian Museum, Cambridge. It 

 is, however, impossible to determine from the description whether 

 any of these are entitled to specific distinction from P. bidlocki, or 

 whether, indeed, they are all referable to this genus, some of them 

 being compared to Hylceochelys latiseutata. 



This species appears to be the most common Purbeck Chelonian. 



Hob. Europe (England). 



46317. The somewhat imperfect and flattened shell ; from the 

 {Fly.) Purbeck of Swanage, Dorsetshire. The carapace is 

 figured by Owen in his ' Wealden and Purbeck Reptilia ' 

 (Mon. Pal. Soc), pt.i. pi. v., and the plastron in pi. vi., 

 under the name of Pleurosternum emarginatum ; the 

 specimen being incorrectly described as being in the 

 collection of Mr. Wilcox of Swanage. The ventral aspect 

 is also figured in Owen's ' Paleontology,' 2nd ed. p. 318, 

 fig. 109, with the omission of the intergnlar shield. This 

 specimen is important as exhibiting the carapace and 

 plastron in connection. The plastron presents no charac- 

 ters by which it can be specifically distinguished from the 

 undermentioned type specimen, although the entoplastral 

 is relatively smaller. The carapace, in which the nuchal 

 is wanting, accords with the next specimen. The 8th 

 neural is confluent with the anterior suprapygal (9 of 

 Owen's figure), although they are represented in the figure 

 as distinct. Cunnington Collection. Purchased, 1875. 



43621. A flattened and somewhat imperfect shell; from the Pur- 

 beck of Swanage. The characteristic form of the nuchal 

 and entoplastral is clearly shown. Purchased, 1872. 



35574. Slab showing the dorsal aspect of the nearly entire carapace ; 

 from the Purbeck of Swanage. The nuchal is relatively 

 narrow ; the 8th neural is distinct from the suprapygal. 



Purchased. About 1 860. 



1 For fuller details on the above-mentioned points reference may be made to 

 the ' Quart. Journ. Geol. Soc.' vol. xlv. pp. 514, 515. 



2 Index to Aves, &c, in Cambridge Museum, pp. 86, 87 (1869). 



