158 BIVALVES. 



species when viewed with either of the slopes in 

 front, exhibits the form of a heart ; indeed all, 

 more or less, approximate to the cordate form ; 

 surface either ribbed, striated, or furrowed longi- 

 tudinally ; margins toothed, the ribs or furrows of 

 the two valves being so arranged as to alternate 

 at the margins, and to fit closely into each other ; 

 the hinge has four teeth in each valve ; the two 

 central are oblique, approximating, and articu- 

 lating with the teeth of the other valve : two 

 lateral teeth remote, inserted ; the beaks are 

 turned inwards ; the umbones are turgid ; the 

 ligament is external. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The Cardium is readily distinguished from 

 the shells of other genera by the peculiarity of 

 its teeth and cordate form ; its ribs or striee also 

 are invariably longitudinal. The mollusca are 

 furnished with two short unequal tubes, fringed 

 with hairs at their extremities ; they have also a 

 muscular foot resembling a bent arm, with which 

 they move their shell. They live buried under 

 the sand, but select a spot near the shore, as 

 they require frequent supplies of water, and to 

 obtain it, are continually protruding their tubes. 

 Many of the species afford nutriment to the 

 poorer classes. The name is derived from the 

 Greek *a< p{ a (cardia) -a heart. 



