65 
OSTREA expansa. 
TAB. CCXXXVIII. — Fig. i. 
Spec. Char. Broads deltoid, angles obtuse, hinge 
pit wide, flat, slightly elevated, and nearly 
straight; cicatrix broad, with a sinus at the 
back. 
XiENGTH 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 laminae 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 Trigoniae, &c. 
OSTREA imdulata. 
TAB. CCXXXVIII.— Fig. 2. 
Spec. Char. Recurved, sub triangular, deep, pos- 
teriorly rounded ; surface radiated ; laminae 
imbricated, undulated ; cicatrix elongated, 
ovate, oblique : hinge pit slightly elevated. 
A more 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- 
minae are very regularly waved over the projecting radii, 
I have only seen the hollow valve. 
