16 EOCENE MOLLUSC A. 



about ten years, but to come to perfection in four or five. Fishermen pretend to be 

 able to tell the age of this Mollusc by the discoloured fimbriations upon the lower valve, 

 somewhat like the hybernating marks upon the snail. 



1. Ostrea adlata, S. Wood. Tab. V, fig. 3, a — c. 



Spec. Char. O. testa minima, ovato-elongatd vel irregularitcr euneatd, apice obliquo ; 

 valvd inferiore radiato-costatd, plus minusve profunda ; valvd superiore planiusculd vel con- 

 oexiuscidd ; marginibus superne granoso-plicatis ; impressione musculari sublunari. 



Shell small, ovately oblong, or irregularly wedge-shaped, apex oblique ; lower valve 

 radiately costated, more or less deep ; upper valve flat or convex, margin near the hinge 

 crenately plicated ; muscular impression sublimate. 



Longest diameter, 1 inch nearly. 



Locality. Hempstead, Isle of Wight {Edwards). 



There is something peculiar about this little shell which seems to entitle it to an isolated 

 position, and I have, in consequence, given it anew name. It is a miniature representation 

 of 0. Jlabellula, but the costae are fewer and do not appear to be visible in the young 

 shell. All the specimens I have seen are attached to Cerithium plicatum ; this, perhaps 

 being the most abundant univalve in the deposit, has been selected for that purpose, and 

 the oyster has sometimes fixed itself in the direction of the height of the univalve, by which 

 it has become elongated from the umbo to the ventral margin, and has thereby altered 

 the natural form of the shell. In one or two specimens the costae are obsolete or scarcely 

 visible, and the margins of the valves near the hinge appear to have interlocked ; 

 having crenulations in the right valve corresponding with depressions in the left for 

 their reception. The cylindrical support of the animal lias not only reduced the depth or 

 capacity of the lower valve, but this internal prominence has communicated its form to the 

 upper valve, making it very convex. It is similar in habit to 0. mutabilis, Desh. Coq. 

 Eoss. des Env. de, p. 344, pi. 56, f. 9-10, but that species does not appear ever to 

 have had its lower valve plicated. 



2. Ostrea aliena, S. Wood. Tab. VIII, fig. 2. 



Spec. Char. 0. testa tenui, ovatd vel ovato-rotundatd, valvd inferiore convexiusculd, 

 extiis irregularitcr costulato-radiatd, sub-lobatd. 



Shell thin, ovate or ovately rounded ; inferior valve slightly convex, and covered with 

 radiating ribs or riblets, and slightly lobed. 



Diameter, 3 inches. 



Locality. Bracklesham {Edwards). 



There are a few specimens of Ostrea in Mr. Edwards's cabinet, which I cannot 

 satisfactorily assign to any species known to me, and I have given to them the above 

 name provisionally. 



