PELECYPOD.i. 



45 



opening and suddenly closing their valves. The species are very 

 numerous, world-wide in their distribution, and may be found at 

 depths from a few to three thousand fathoms. 



The Limas (Limidce) are very like the Pectens, but the inner edge [Case 

 of their mantle is fringed with very long thread-like filaments. The 25 F 'J 

 shells are always white, generally more or less oblique, and radiately 

 ridged. They appear to be found in most seas, and either swim 

 about freely like the young Scallops by flapping their valves, or 

 attach themselves by a byssus, sometimes forming a sort of nest, 

 consisting of pieces of coral and shell or small stones, in which 

 they are completely concealed. 



The Ostreidce, or Oysters, undoubtedly take the first rank [Case 25 



F-H.] 



Fisr. 31. 



y 



d"' f 



Common Edible Oyster (Ostrea edulis). 



a, labial palpi ; b, gills ; c, mantle ; d, junction of the two folds of the 

 mantle ; e, large adductor muscle ; /, the shell. 



among mollusks as regards usefulness to mankind as an article of 

 food. They have no foot ; the mantle is entirely open, with double 



e 2 



