143 
0STREA laeviuscula. 
TAB. CCCCLXXXVI1I.— /g. 1. 
Spec. Char. Depressed,, rounded, triangular; sur- 
face obscurely imbricated, smooth ; beak 
acute ; scales distant. 
V ery similar to the O. edulis, but smoother : the beak 
is pointed and turned backward ; the lower valve is not 
ribbed, but very smooth ; in the specimen figured it is 
attached by nearly its whole surface to what appears to 
be a fragment of a large Pinna, and the edges are ele- 
vated. 
From the upper beds of the Lyas Clay at 
OSTREA obscura. 
TAB. CCCCLXXXVIII.- jig. 2. 
Spec. Char. Oblong, uneven, small ; lower valve 
very deep, the other flat ; beak curved. 
A diminutive species of Oyster (much resembling Gry- 
phaea nana, tab. 383 ) : its small size, oblong form, and 
deep valve are, when taken collectively, sufficient to di- 
stinguish it from every other : in some specimens the 
hinge pit is so much produced and curved as to prove 
that they are not young shells. 
The Ancliff Limestone, so celebrated for pigmy shells, 
contains an abundance of these little oysters, associated 
with so many other genera that a description of them 
alone would almost form an introduction to a system of 
Marine Shells. 
OSTREA costata. 
TAB. CCCCLXXXVIII- fig. 3. 
Spec. Char. Orbicular; lower valve deep, ribbed; 
ribs numerous, branched ; upper valve flat, 
with an undulated margin. 
Branching, rounded ribs upon the under surface de- 
fine this neat little Oyster. It is one of the miniature 
productions of the Ancliff Limestone. 
