LUCINA. 75 



A remarkable circumstance noticed with regard to the 

 Cardia is, that those which inhabit sheltered localities have 

 much thinner shells than those which lie in coarse sands, 

 exposed to tidal currents ; the covering strengthens in pro- 

 portion to the amount of protection required, just as a well- 

 known long-eared and patient quadruped is assisted in 

 bearing the violence to which he is exposed, by being pro- 

 vided with a remarkably thick skin; or as some among 

 mankind, having to encounter much rough treatment in the 

 world, are mercifully guarded by an extra degree of ob- 

 tuseness, an outer coating of hardiness, suited to their state. 



LUCINID^aS. 



I. LuciNA, the genus from which the family is named, has 

 generally a round form, with a remarkably long foot, ca- 

 pable of being contracted within the mantle, which is 

 open and fringed; the siphons are "sessile," that is, 

 not protruding. The shell is generally white, rounded, 

 has no sinus in the impression of the mantle, but a 

 curious elongation of the anterior muscle. Of the 

 British species, — as to the shells, 



L. borealis is the largest; it is round and regularly ridged 

 in a circular direction. 



