42 TRANSACTIONS, NATURAL HISTORY SOCIETT OF GLASGOW. 



VI. 



ISOCARDIA COR, L., IN THE WEST OF 

 SCOTLAND. 



BY ALEX. SOMERVILLE, B.SC, F.L.S. 



With one Plate [I.]. 

 [Read 30th October, 1888.] 



The marine bivalve mollusc Isocardia cor, L., is the 

 only British species of the eccentric genus to which 

 it belongs. The recent Isocardice (including the 

 section Meiocardia) known to science number some 

 five only, their distribution being the Scandinavian 

 and British seas, the Mediterranean, and the seas of 

 China and Japan. In fossil times Isocardice were 

 more plentiful, both in kind and number, than now ; 

 for we find some 90 species in all, which have been 

 referred to this genus, scattered through various 

 formations from the Lias downwards to the Crag 

 and other Pleiocene strata. 



Isocardia cor is certainly a shell of exceptional 

 appearance, its cordate-globular form rendering it 

 both striking and elegant. It differs from the shells 

 of all the other 160 lamellibranchs that inhabit 

 British seas, in that while they (including the 

 only other species of the family to which Isocardia 

 belongs, viz., Cyprina islandica, L.) have the um- 

 bones or beaks simply incurved in the usual manner, 

 the beaks of Isocardia are considerably apart, grace- 

 fully recurved, and, indeed, so spirally twisted as to 

 form a nearly complete whorl. Linnaeus called the 

 shell at first Cardiutn humanum from its resem- 

 blance to the human heart, then Chama cor ; 



