OSTREA. 39 



Var. 2. Tiippapus. Shell large and extremely thick. 0. 

 Irippopus, Lam. An. sans Yert. vii. p. 219. 



Var. 3. deformis. Shell small, distorted, and often nearly 

 cylindrical. 0. deformis, Lam. 1. c. p. 229. 



Var. 4. Rutupina. Shell small, transversely oval and of a 

 regular shape. 



Var. 5. tincta. Shell flattened and attached in every stage 

 of growth ; inside of a rich purplish-brown or olive-green ; 

 hinge-margins strongly crenulated. 



HABITAT : 0-45 fathoms, on every part of our coast 

 from Shetland to the Channel Isles, usually gregarious 

 and forming beds of various extent. Var. 1. On shells, 

 crabs, and other substances, having rather a more south- 

 ern distribution. When this variety is affixed to a ribbed 

 scallop, it adopts the markings of that shell, but it re- 

 tains its own colour. It appears to be the O. depressa 

 of Philippi. Yar. 2. In deep water and solitary. Var. 3. 

 Occupying the crevices of rocks in the littoral and 

 laminarian zones, and called the " rock-oyster." Some 

 specimens resemble a Gryphcea in shape. Var. 4. Coasts 

 of Essex and north Kent, in a semicultivated state, and 

 well known in this country as " natives." Var. 5. West 

 of Scotland and Burra Isles, Shetland. Mr. Grainger 

 has noticed this ubiquitous species as " imbedded in 

 considerable myriads" in a raised pliocene deposit at 

 Belfast; and, according to Mr. James Smith and Mr. 

 Geikie, it occurs in the Clyde beds and other glacial 

 deposits in Scotland. Red and Coralline Crag (S .Wood) . 

 The shells may also be seen mixed with those of pecu- 

 liarly arctic species in the raised sea- beds near Udde- 

 valla. It is very difficult to ascertain its foreign distri- 

 bution, with any tolerable degree of correctness, in con- 

 sequence of its specific identity being enveloped in such 

 a cloud of different names. Depending, however, on 



