78 



Shell Life 



architecture is rich in angles, sharp edges, and spines, 

 to serve various purposes in their lives ; but the Pea- 

 crab has given itself up so whole-heartedly to the 

 comfort of its friend that it has got rid of every 

 angle, every sharp edge, every spine and stiff hair. 

 All its parts are rounded, and polished with a surface 

 like glass, so that the movements of this strange 

 little crustacean between the gills of the Pinna 

 cannot cause injury to the very delicate tissues of the 

 moUusk. 



The Oysters are represented in our fauna by the 

 solitary species which has from the earliest human 

 period been regarded as a luxury, because the demand 

 appears always to have exceeded the supply ; and 

 concerning whose structure, growth, artificial cultiva- 

 tion, and commercial value very much has been 

 written. 



The Common Oyster (Ostrea edulis) needs little 

 description, its shell being at least as familiar in the 



streets of inland cities as 

 it is on the seashore. 

 Attention may be called 

 to the fact, however, that 

 the valves are not equal 

 in size or form, the lower 

 (left) being larger and 

 convex, and the upper 

 (right) is flat or slightly 

 concave. Whilst the left 

 is frequently marked by 

 overlapping plaits, folds, 

 and flat spines, the right is usually plain. The shell 

 of the very young Oyster is round in outline, but 



Oyster, with right valve removed 



