ill 
OSTREA deltoidea. 
TAB. CXLYIIL 
Spec* Char. Equivalved, flat, thin, orbicular, 
with a deep sinus on one side, and a produced 
straight beak, 
Syn. Ostrea deltoidea, Lamarck Env . de Paris , 
p. 265, __ _ 
So flat is this oyster that there is very little room for an 
animal between the shells ; the back part is elongated 
with parallel sides for a short space, forming a kind of 
neck terminated by the hinge : the pit of the hinge is of 
equal width withit: the front is rounded and produced on 
one side in a lobe which, together with the beak, forms two 
angles of a triangle, and gives the outline the general 
form of the letter D or A ; the shell is thin, the edges 
extend far beyond the interior surface, especially about 
the neck, and make the external outline more orbicular 
than the internal. 
This oyster is a sort of proof of a characteristic con- 
stancy in shape that nothing can contradict, however, we 
might suspect otherwise in so variable a Genus ; thus this 
species is known to all who have once recognized it, 
without any difficulty. The extreme flatness,* even 
when the shell is attached to more gibbous species, were 
it not constant, might be attributed to some pressure, for 
the space that the animal might have occupied seems in- 
sufficient to have allowed of its existence, and the shell 
possessing the usual characters of its tribe, the tripartite 
hinge, the multiplied lateral laminae, &c. we should have 
* Connecting the idea of flatness where there is much variety of colour 
is sometimes mere difficult than might be expected, m dark tints gene- 
rally serve f@r relief. 
