179 



CORBULID^. 



This tribe is composed of bivalves, all of comparatively 

 small dimensions, the majority very small. Most of them 

 have inequivalve shells, and all have their hinder extre- 

 mities more or less produced, and easily distinguished by 

 the tendency to form a beak from the anterior or buccal 

 end. The last mentioned is the most constant character, 

 for the hinge, presence or absence of epidermis, thickness 

 and sculj)ture of shell, and even position of the ligament, 

 vary considerably in the several genera composing the 

 "tribe. The animals of all, however, are very nearly allied, 

 and easily distinguished, for all have extremely short 

 united siphons, with fimbriated extremities, the anal one 

 always provided with a conspicuous membranous tube. 

 The mantle is closed, except a passage for a narrow foot, 

 not unlike that of the GastroclKEnidce^ to which family the 

 Corhula tribe has very close affinity. Most of the British 

 members of this tribe are either rare or very recent disco- 

 veries, and several of them we have to figure for the first 

 time as natives of our seas. 



CORBULA, Bruguiere. 



Shell suborbicular or oval, tumid or depressed, very in- 

 equivalve, slightly inequilateral, rounded anteriorly, more 

 or less truncated posteriorly ; beaks prominent ; surface of 

 the valves more or less furrowed or transversely striated, 

 covered with an epidermis. Hinge composed of a recurved 



