L90 CRETACEOUS LAMELLIBliANCHIA. 



L850. Venus Eicordeana, A. d'Orbigny. Pro&f. de Pal., vol. ii, p. 76. 



1855. G. Ootteau. Moll. Foss. de l'Yoime, p. 64. 



L865. F. J. Pictet and G. Canqnclie. Foss. Terr. Cret. Ste. 



Croix (Matc'r. Pal. Suisse, ser. 4), 



p. 169. 

 1870. F. Stoliczka. Palseout. Indica, Cret. Fauua S. India, 



vol. iii, p. 159. 



Description. — Shell oval, convox with flattened sides, considerably inequilateral, 

 anterior part higher than the posterior part. Anterior margin regularly rounded, 

 passing gradually into the slightly curved ventral margin. Postero- dorsal margin 

 long, convex, with a considerable ventral slope. Posterior margin short, oblique, 

 forming a rounded angle with the ventral margin. Umbones broad, curved 

 forwards. The part of the shell behind a line between the umbones and the 

 postero-ventral angle slopes rapidly from the flattened sides. Lunule elongate, 

 limited by a groove. Escutcheon elongate, deep, limited by a sharp edge. 



Ornamentation consists of sharp concentric ridges. Pallial sinus angular, 

 somewhat ascending. 



Measurements : 













(i) 



(2) (3) 



(4) 



(5) 



Length 



56 



52 . 52 



50 



43 mm. 



Height 



47 



40 . 39 



(1) Atherfield Beds, Peasmarsh. 

 (2, 5) Perna-bed, Atherfield. 



(3) Hythe Beds, Lympne. 



(4) Hythe Beds, Pulborough. 



35 



34 „ 



Affinities. — -English specimens differ from d'Orbigny's figure in the more rapid 

 ventral slope of the postero-dorsal margin. I am indebted to Professor Boule for 

 comparing photographs of specimens from the Lower Greensand with the examples 

 in the d'Orbigny collection which appear to be the types, and he states that in 

 the latter the shell is less elongate and the postero-dorsal border has a greater 

 slope than in d'Orbigny's figure, consequently the photographs agree much more 

 closely with the types than with the figure. M. A. de Grossouvre has been good 

 enough to lend me a specimen of 0. (Flaventia) Ricordeana from the Lower Aptian 

 of Seignelay, Yonne, one of the localities mentioned by d'Orbigny, and a 

 comparison of that with English examples leaves no doubt as to their specific 

 identity. 



The generic position of dementia (Flaventia) Ricordeana is at present some- 

 what uncertain since none of the specimens shows the hinge ; but on account of 

 the resemblance in the form of the shell to that of 0. (Flaventia) ovalis it is 

 probable that this species belongs to the sub-genus Flaventia. 0. (Flaventia) 



