96 POPULAR BRITISH CONCHOLOGY. 



folds of the sedentary P'mna's sliell. They will thus be able 

 to account for their existence in such a situation^ without 

 resorting to the curious old fable about the crustacean pro- 

 viding food for the mollusc, as a rental for his apartments 

 in the shelly tenement, and the " entente cordiale" between 

 them. 



THE ABCADJE 



crawl on the expanded surface of the foot, which, when not 

 in action, has its two sides wrinkled up so as to form a 

 groove j an open mantle ; and a shell which, however different 

 in form, always has on the hinge a row of interlocking teeth. 

 I. NucuLA has the disc of the foot sharply notched; the 

 pretty little shells are very bright and pearly, with two 

 half-circular rows of sharp teeth on the hinge; a very 

 sober drab -coloured epidermis without. The shells of 

 the British species are — 

 N. decussata : rather oval, finely striated ; dorsal area sculp- 

 tured. 

 N. radiata : smooth, more oblique, rayed. 

 N. teriuis : thin, smooth, inner edge not crenated. 

 N. nucleus : rather triangular, smooth, blunt at the hinder 

 end ; epidermis dull. 



