LUCINA. 43 



will be seen hereafter, it differs in having the branchial 

 lamellae not united on each side, and the labial palps fully- 

 developed. 



LUCINA. Brugiere. 



Shell eqnivalve, orbicular, sub-compressed or tumid, 

 regular, often nearly equilateral ; surface smooth or con- 

 centrically striated, or ribbed in one or both directions, or 

 marked with undulating or angular furrows ; hinge very 

 variable, usually presenting two diverging cardinal teeth 

 and two laterals, but in many species one or both sets of 

 teeth are more or less obliterated ; ligament varying in 

 position, chiefly external ; muscular scars strongly marked, 

 the anterior usually elongated ; pallial impressions simple. 



Animal orbicular, its mantle freely open in front, with 

 plain or fimbriated edges ; siphonal orifices sessile, the anal 

 sometimes (always 1) provided with a retractile produced 

 tube (anal valve ?). Foot very long, ligulate, tubular. 

 Branchial leaflets of each side united into one ; labial palps 

 obsolete. 



The assemblage of shells to which the name Lucina has 

 been given by conchologists includes so many species, pre- 

 senting striking dissimilarities in dentition and sculpture, 

 that we are naturally tempted to separate them into distinct 

 generic groups, and many appellations of j^roposed generic 

 value have been given to their several supposed types. Un- 

 fortunately, however, our knowledge of the animals of the 

 so-called Lucincc is by no means commensurate with our 

 acquaintance with their shells, and all that we do know 

 would rather seem to warn us against the proposed divisions 

 than to bear them out. It appears as if many important 

 characters, which in other families afford almost unfailing 



