65 
OSTREA expansa. 
TAB. CCXXXVIII.—Fig. 1. 
Spec. Cuan. Broad, deltoid, angles obtuse, hinge 
pit wide, flat, slightly elevated, and nearly 
straight; cicatrix broad, with a sinus at the 
back. ; 
Vucxeru and breadth nearly equal; the margin is 
largely waved: I am not acquainted with the outside of 
the shell. 
There is a remarkable circumstance connected with 
this and the following Oyster; but most strikingly in 
this; it is, that the softer part of the shell under the 
ligament, has resisted the action of the solvent, that in- 
troduced Silex in place of the chalky substance between 
the lamin in the other parts of the shell, but has sub- 
sequently decayed away, leaving an inclined hollow 
space reaching nearly to the beak. 
These remains are found in the Tisbury Limestone, 
accompanied by empty casts of Trigoniz, &e. 
OSTREA undulata. 
TAB. CCXXXVIII.— Fig. 2. 
Spec. Cuan. Recurved, subtriangular, deep, pos- 
teriorly rounded ; surface radiated; lamine 
imbricated, undulated; cicatrix elongated, 
ovate, oblique: hinge pit slightly elevated. 
A wore regularly formed shell than what usually be- 
longs to an Oyster; it is thick, and at the beak retains 
marks of attachment to some uneven surface; its la- 
minz are very regularly waved over the projecting radii. 
T have only seen the hollow valve. 
