BIVALVIA. 25 



specimens of the upper valve of gigantea, from Barton. This structure is not, in general, 

 so evident in the lower or left valve, where the exterior generally appears foliaccous; 

 but the carious structure may be observed, where there is a fracture. The Barton 

 specimens appear to have adhered broadly. Dr. Bowerbank's specimen, from 

 Bracklesham, exhibits scarcely any mark of attachment. One of my specimens, 

 from Barton, had been fixed to a cylindrical body, which has imparted to the upper valve 

 a semi-cylindrical elevation like that characteristic of dorsata, which it much resembles ; 

 and the outer surface, where it is preserved, is covered with fine radiating striae, which 

 are occasionally in ridges, like those represented upon 0. oblonga, Brander, PI. VII, fig. 83. 

 I suspect that this last specimen was only an imperfect individual of the present species. 

 There is a great tendency to thickening of the shell in those from Bracklesham. One 

 aged specimen in Dr. Bowerbank's museum has the following dimensions : — diameter, 5 

 inches by 4, thichiess of shell in this lower valve, two inches and four tenths. 0. cattifera 

 (from Cutch), J. Sowerby (Tran. Geol. Soc, vol. v, pi. ii, second series, pi. xxv, fig. xvi), 

 is a shell in that state, probably belonging to this species. 



Ostrea cariosa is given by Professor Morris, in his catalogue, as a British fossil ; and it 

 is also introduced by Mr. J. D. C. Sowerby, in Dixon's ' Geology of Sussex,' pp. 117, 226 ; 

 I have not seen a specimen on which this specific isolation might be founded. May it 

 not be the young state of gigantca ? as suggested by Mr. Sowerby. 



11. Ostrea gryphovicina, S. Wood. Tab. VII, fig. 6, a, b. 



Spec. Char. 0. testa crassd, ovatd ; valvd inferiore ttimidd, profunda, obsolete lamellatd ; 

 calvd super iorc planiusculd, nudd ; cardine magno, trigono, fossuld ligamenti august issimd, 

 excavald ; uiarginibus integris ; impressione musculari subrotundd, parvd . 



Shell thick, ovate ; lower valve tumid and deep, with almost obliterated lamella) ; 

 upper valve flattened and nearly smooth ; hinge area broad, with a long, narrow, and 

 deep ligamental furrow ; margins free from crenulations ; muscular impression round and 

 small. 



Height, %\ inches. 



Localities. Sheppey (Boicerbank), Hampstead {Wether ell). 



The peculiarly deep, contracted, and elongated ligamental pit in these shells differs from 

 any other that I have seen, and gives reason to believe that they belong to a distinct species ; 

 the shape of the muscle-mark appears also to be different from any other. In the specimen 

 belonging to Mr. Wetherell there is an obtuse lateral lobe separated by a shallow sinus 



* On requesting Dr. Carpenter to give me his opinion upon this peculiar appearance, he says : — " I think it 

 likely that the structure you allude to is one which I have seen in various large oysters, both recent and 

 fossil, and which was first noticed, I believe, by Dr. J. E. Gray, namely, a cancellated tissue filling up the 

 space that would otherwise be left empty between separated lamellae." 



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