42 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



am now inclined to think that this form is so far distinct from the common edulis that it 

 should be separated from it. The O. edulis of our coasts has the lower valve always 

 more or less covered with imbricated radiations, of which the Cor. Crag shell is destitute, 

 or on which, at least, they are obsolete or nearly invisible. The common form of our 

 edible Oyster has not come under my. observation, either from the Coralline or from the 

 Red Crag. Eigs. a and 2 b of Tab. II, ' Crag. Moll.,' may possibly be the immature 

 state of '. _princeps : Our edible Oyster is described in 'Brit. Conch.,' vol. ii, p. 38, as 

 having the " hinge-line narrow and nearly straight," " lateral edges (especially of the flat 

 valve) finely crenulated or notched on the upper part;" but the Cor. Crag shell is destitute 

 of these, and the depression left by the connector is greatly incurved; I have, in 

 consequence, had the outside of the lower valve, as well as the place of the connector 

 figured. 



The Cor. Crag shell is very thick and ponderous ; and in that respect it resembles 

 the more southern form of edulis, which Lamark described as a species under the name 

 of Ostrea hippopus. It, however, corresponds better with the Oyster from the Antwerp 

 beds, which is figured by M. Nyst under the name ungulata, var. a. 



M. Nyst says of this shell (p. 826 of his work), " La var. a est plus bombee. Les 

 sillons longitudinaux ont entierement disparu sur les deux valves," but in his figure he 

 has represented these " sillons " (radiations) obsolete or obscure, like they are on our 

 Cor. Crag, shell. He gives the localities of 0. ungulata as Anvers and Bognor, but does 

 not specify the special locality for var a. The form in his pi. xxiv, fig. 1, is, however, 

 probably 0. Bellovacina from Bognor, while var. a is presumably from Anvers ; and on 

 that assumption I have referred our Crag, shell to it, for it is certainly not the Eocene 

 Bellovacina. 



In the ever recurring difficulty as to whether shells in the Red Crag belong to that 

 formation, or are only derivative in it, it is impossible to say whether this shell, of which 

 specimens have occurred in the Red Crag, belongs to the age of that Crag or not ; but I 

 have not met with the true form of the British 0. edulis in the Red Crag. 



I do not think now that the shell figured in my first Supplement, Tab. VIII, as 

 Ostrea jilicatula is the same as the shell here figured as ungulata. 



Mytiltjs edulis, var. galloprovincialis. 2nd Sup., Tab. VI, fig. 9. 



Mytilcs gaulopeovincialis, Lam. An. Sans. Vert., t. vii, p. 46. 



— — Phil. Moll. Sic, vol. ii, p. 53, t. vi, figs. 12, 13. 



Locality. Red Crag, Sutton. 



The specimen of this peculiar form, above figured, has been obtained by Mr. Edward 

 Aloore, of Woodbridge, from the Bed Crag as above. 



