266 CARDIID^E. 



ments : gills short ; upper pair smaller than the lower : palps 

 triangular : foot sickle-shaped. 



SHELL convex, closed in nearly every case : beaks bent in- 

 wards, but scarcely (if at all) to one side : teeth, in the right 

 valve usually two cardinals, besides two laterals on the ante- 

 rior side and one on the posterior side ; sockets deep : inside 

 more or less fluted, and having the margin notched. 



This genus is redolent of the good old times. It 

 carries with it a smack of true conservatism progressive 

 improvement without innovation. Every sound con- 

 chologist must rejoice at seeing the name of Cardium 

 still preserved, with a few others, and to know that 

 they have survived the extensive and often injudicious 

 changes which systematists have been continually pro- 

 posing since the death of the much-honoured Swede. 

 Some corrections arid modifications of his scheme of 

 classification were required by the progress of science, 

 and they have been made. With regard to our own 

 molluscan fauna, C. corneum, C. lacustre, C. amnicum, 

 C. rubrum, C. discors, and C. arcuatum of Montagu 

 have been placed in very different families, and a few 

 species have lately been added to the British list. But 

 the genus has a solid foundation, and is likely to last as 

 long as conchology itself. 



Its large and fleshy foot is admirably adapted for 

 penetrating and burrowing into sand. The mode by 

 which this operation is effected has been well described 

 by Reaumur. He says that when the animal wishes to 

 sink, it lengthens its arm [or foot], and at the same 

 time attenuates the extremity of it, which thus becomes 

 almost pointed. With this it makes a hole, like a 

 gardener using his dibble, and buries the arm in the 

 sand, continuing the perforation with the pointed end ; 

 and by repeatedly lengthening and contracting this 

 muscular organ, it in a short time works the shell below 



