143 



^ OSTREA Iseviuscula. 



TAB. CCCCLXXXVIIL— /g^. 1. 



Spec. Char. Depressed, rounded, triangular; sur- 

 face obscurely imbricated, smooth ; beak 

 acute ; scales distant. 



Very 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. CCCCLXXXVIIL— /g-, 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. 



— B^ 



OSTREA costata. 



TAB. CCCCLXXXVIII — /g^. 3. 



Spec Char. Orbicular; lower valve deep, ribbed; 

 ribs numerous, branched ; upper valve flat, 

 with an undulated margin. 



Jdranching, rounded ribs upon the under surface de- 

 fine this neat little Oyster. It is one of the miniature 

 productions of the Anclifi* Limestone. 



