CARDIUM. 



are concerned, to be perfectly natural; and we have no 

 doubt, that if the animals of all these species were known, 

 they would be found fully to evidence the propriety of it.* 



That a Genus of so great importance should be passed 

 over with so few observations may perhaps appear strange, 

 but it really presents itself to our view with so few 

 encumbrances, that we have nothing more to say or do 

 than to describe the characters peculiar to the Genus and 

 give a somewhat detailed view of the principal external 

 forms included in it, and, stating some particulars relating 

 to the characters and habits of its animal, conclude with 

 such information as we have relating to its fossil species. 



The species of the Genus Cardium must be described 

 as equivalve, although there is always a slight difference 

 in the form of the two valves : they are nearly equilateral, 

 and more or less gaping posteriorly: the outer surface of 

 some few of the species is smooth and shining, but for the 

 most part they have more or less strongly marked ribs, 

 radiating from the umbones to the margins: inner margins, 

 except close to the hinge surrounded by larger or small 

 teeth or crenulations according to the size of the radiating 

 ribs, those species which have no ribs, having neverthe- 

 less very fine teeth round the inner margin. Cardinal 

 teeth in each valve two, placed very near together, 

 oblique, and locking into each other cross- wise : there are 

 also two remote, lateral, teeth in each valve :t muscular 

 impressions two in ea<!h valve, lateral, distant: muscular 

 impression of the mantle entire. Ligament external. 



We have stated that the Cardia vary much in general 

 form ; thus, some species are nearly glohidar, such for 

 instance as the C. tuberculare ; some are deeper than they 

 are long or wide, such as C. biradiatum : some are longer 

 from front to back than in any other direction, one of 

 these has been called C. soleniforme ; others have a pro- 

 minent nearly central ridge commencing at the umbones 



* It will be observed by some that we here write upon purely concholo- 

 gical principles. Cardium must be regarded as a natural Genus, even by those 

 who cannot consent to the formation of a natural system, founded upim the 

 combined consideration of the animal inhabitants in connexion with the shells, 

 which we are nevertheless persuaded can alone be the foundation of the natu- 

 ral system. 



\ One species is remarkable for being almost destitute of teeth, it is 

 the Cardium edentulum, Lam. 



