496 BEY. G. E. WHIDBORNE ON SOME EOSS1LS 



raised spiral edge, Muscle-mark circular, almost iu the exact 

 centre of the posterior aspect. 



From the lower green bed of the Northamptonshire Oolite. Two 

 specimens in the Sharp Collection in the British Museum, probably 

 from Duston. 



Dimensions. 4 lines. 



The only remaining parts are moulds of the left valves. Its 

 distinct reflected umbo at once distinguishes it from G. mima, Phill., 

 while, according to Morris & Lycett, Eocogyra auriformis, Goldf., 

 has a large adhering surface on its left valve, and its right valve 

 has a flat and subspiral but very much larger umbo. 



Exogyra lingulata, Morr. & Lye. pt. 2, t. 32. fig. 2, is a much longer, 

 narrower, and larger shell. Brown, however, in his ' Fossil Concho- 

 logy,' t. 61. figs. 10-12, and p. 149, gives a shell which is much 

 nearer the present species. This shell, Gryplvxa minuta, Sow., Min. 

 Conch, t. 547. fig. 4, as figured and described in Lycett's Supple- 

 ment, differs by having a much larger and more direct beak, which 

 is " closely pressed," and a more rounded and flatter surface. 

 Though Sowerby's own figures are more like, his original specimens 

 in the British Museum show that though it is an Exogyra, its umbo 

 is much more terminal, and its anterior side more expanded, so that 

 its mould would be flatter and less defined. 



Plactjna Rupeetina, n. sp. Plate XY. figs. 16, 16 a. 



Left valve convex, very thin. Hinge-line small, wide, eden- 

 tulous, transversely striated. Cartilage-grooves small, narrow, con- 

 cave, equal, each inclined at an angle of more than 45° to the per- 

 pendicular. Between these and the hinge are two oblique raised 

 spaces or rounded ridges penetrating the general concavity of the 

 interior for a short distance. Muscular impression long, narrow, 

 but slightly expanding as it extends from the hinge two thirds down 

 the centre of the shell, where it ends with a slight curve forwards, 

 and defined by a slightly raised boundary line. Umbo acute. Hinge- 

 area bounded by short straight lines. Anterior margin very convex, 

 posterior nearly straight, postero-inferior corner subangular. Sur- 

 face most convex near posterior side. 



Dimensions. Length 3 inches, width 2| inches, depth 1 inch. 



One specimen in the Sharp collection in the British Museum, 

 from the Inferior Oolite of Duston. 



This specimen is only a cast, but it appears to give all the cha- 

 racters of the shell except the exterior markings, and to be so re- 

 markable as to be worth noticing. It does not belong to Lycett's 

 genus Placunopsis, which differs in having a single and central car- 

 tilage-groove, and in the style of the muscular impression, while the 

 species described by him under that genus are all very much smaller 

 and of different contour. 



On the other hand, Prof. Rupert Jones (after whom I have the 

 pleasure of naming it) having labelled it " allied to Placuna of Indian 

 and Chinese seas," and Mr. Etheridge having very kindly compared 

 it with recent specimens, there remains. I think, no doubt that it 



