BIVALVIA. 17 



The principal distinction is the thinness of the shell and the suiallness of the hinge- 

 area, with rather small and distant ribs in which characters, as well as in the form of 

 the muscle-mark, it seems to differ from the young of 0. Bellovacina, to which it other- 

 wise somewhat approaches. I have not seen the upper valve. 



.'3. Ostbea BellovacinAj Lamarck. Tab. Ill, Jig. 1, a, b, and Tab. VII, fig. 3, a — c. 



Ostrba Bellovacina. Burtin. Oryct. de Brux., pi. 10, tigs. « — d, 1784. 



— Lam. An. du Mas., t. viii, p. 159 5 and t. xiv, pi. 2~>, fig. 1, <>, b, 



1806. 



— — J. Sowerby. Min. Conch., t. 388, figs. 1, 2, 1823. 



— — Deshayes. Coq. Foss. des Env. de Par., p. 35G, pi. 48, figs. 1, 2; 



pi. 49, figs. 1, 2. 



— Goldf. Petr. German., t. 11, p. 15, pi. 77, fig. 2. 



— Nyst. llecli. Coq. Foss. de Iloesselt and Kl. Sp., p. 10, A T o. 11, 



183G. 



— — Nyst. Coq. Foss. Belg., p. 318, pi. 30, fig. 1, a; pi. 31, fig. 1, b ; 



pi. 32, fig. 1, a ; pi. 33, fig. 1, b ; 1813. 

 edulina, Lam. Hist, des An. sans Vert., t. vi, p. 218, 1822. 



— — J. Sowerby. Min. Conch., t. 388, figs. 3, 4, 1823. 



— undulata? J. Sow. (non Nyst). Min. Conch., t. 238, fig. 2, 1819. 



Spec. Char. 0. tcstcl ocatd, depress) uscutd, valcd inferiore conrexd, radiatim et rugose 

 costatd, et squamoso-foliaced ; valcd superiore planatd, obsolete radiatd; concent rice lamellald; 

 impressione muscutari mediocri, ovato-semitunari ; umbonibus sub<cqnalibus. 



Shell ovate, rather depressed, lower valve convex, with rugose, radiating ribs or ridges 3 

 foliations sqnamose ; upper valve nearly flat, and obsoletely ridged by lamellated lines 

 of growth ; muscular impression of a moderate size, ovately lunate ; umbones nearly 

 equal. 



Longest diameter. 4 inches. 



Localities. Charlton, var. a, Dulwich, car. (3 {Edicards). 

 France, Hauteville, Beauvais {Lamarck). 

 Belgium, Kleyn-Spauwen, Hoesselt et Lethen {Nyst). 



Oysters occur almost throughout the whole extent of the lower beds of the Eocene 

 Formation in England, and all the specimens that have been found were for a long time 

 considered by geologists as varieties of 0. Bellovacina, and the geographical range assigned 

 to this species extends from Clarendon, Pebble Hill, and Newbury, through Reading, to 

 Northaw and Rochester, including within these outskirts the central portions of Woolwich, 

 New Cross, &c. On expressing an opinion to my friend, Mr. Prestwich, that there were 

 two species found in these lower beds, and my wish, if possible, to have them separated, 

 and their proper localities assigned, and requesting his assistance for that object, I learnt 

 from him that he had, since the publication of his paper, strongly suspected that the 



3 



