Z CARDIAD^. 



and is probably parallel with the Luc'midft, which we are 

 compelled to treat of in sequence. 



CARDIUM, LiNNiEus. 



Shell equivalve, more or less cordiform, oblong, or trans- 

 versely ovate, usually inflated, closed or gaping posteriorly, 

 longitudinally ribbed or furrowed in radiating fashion from 

 the prominent beaks, rarely smooth ; ribs often scaly or 

 spiny ; margin almost always crenulated. Hinge composed 

 of two oblique primary teeth in each valve, and two remote 

 lateral ones (in certain exotic forms the teeth become par- 

 tially or wholly obsolete). Ligament short, external, con- 

 spicuous ; pallial impression simple. 



Animal suborbicular, tumid, its mantle freely open in 

 front, with plain, or, less frequently, fringed edges, conspi- 

 cuously fimbriated in the neighbourhood of the two very 

 short, slightly-separated siphons, the branchial one of which 

 is always fringed at the orifice. Foot very large, cylindri- 

 cal, geniculated. Branchial leaflets unequal, labial palps 

 rather long and triangular. 



This great and very natural genus preserves its Linnsean 

 constitution, and every day receives accessions to its ranks 

 from the researches of zoologists investigating distant re- 

 gions. The shells composing it are often remarkable for 

 their elegance of form and brilliancy of colouring, and even 

 our few British species are among the handsomest of our 

 bivalve mollusks. There is a pleasure in investigating a 

 group such as this, wherein we find not only the greatest 

 variety, but also the greatest distinctness, and consequent 

 certainty of specific determination. All that is known as 

 yet of the animals of the several species goes to indicate 

 that the features they present are as distinct as those ex- 

 hibited by their shells. 



