12a 



with much obliquity and the anterior lobe strongly 

 marked ; the sides of the straight hinge frequtntly have 

 teeth, or crenulations, similar to those that often occur 

 in common Oysters ; besides the principal muscular im- 

 pression in each valve, there is a smaller one near the 

 hinge, which is much more conspicuous than in any 

 Oyster I have observed it in : this has not escaped 

 the notice of the Artist who drew the excellent figures 

 for Cuvier and Brogniart's Geology of the environs of 

 Paris. 



Found in Chalk wherever it occurs, and not confined 

 to the upper beds. It is also met with in the Chalk 

 Marl. Lamarck's unfortunate repetition of this species, 

 under two genera has made it adviseable to give it an 

 entirely new name ; the specific name vessicularis, too 

 nearly resembles vessiculosus, which has been used else- 

 where (see tab. 369) rather inadvertently, but it is 

 to be hoped appropriately. Brogniart's quotation of 

 G. dilatata, M. C. 149, it is hardly necessary to observe 

 is quite erroneous, that species never occurs in Chalk. 



Our specimens are mostly from Norwich, through the 

 kindness of the Rev. G. R. Leathes ; this is the same 

 place that furnished Smith with the specimens figured 

 in his work upon Strata identified by Fossils. 



The Genus Podopsis, to which Lamarck has referred 

 this shell, was established by De France, and ap- 

 pears to include the same shells with Dianchora of Min. 

 Conchology ; in fact his Podopsis striata, is the Dian- 

 chora lata of Min. Conch, tab. 80. which being taken 

 from an inferior specimen, was probably overlooked ; the 

 characters of the two Genera are of course the same : the 

 shell before us having no opening in the beak cannot be 

 a Podopsis. 



