98 



Family 5. CARDIACEA. 



Shell ; equivalve, mostly ventricose and heart-shaped, and, with 

 rare exception, radiatcly ribbed ; hinge composed of two strong 

 cardinal teeth in each valve ; lateral teeth variable ; ligament 

 external. 



The family Cardiacea is constituted of the well-known genus of Cockles, 

 Cardium, added to on the one side by two exotic genera, Cypricardia and 

 Cardita, which show affinities with Chama ; and by the Heart Cockles, Iso- 

 cardia, on the other, which are more allied to Cyprina. The hinge of the 

 shell is composed of rather strongly-developed cardinal teeth, with, fre- 

 quently, an elongated lateral tooth on one or both sides. The animal of 

 this family varies in a manner which renders the association of these genera 

 less satisfactory. In Cardium the mantle-lobes are freely open in front for 

 the passage of a large and active foot, and closed behind with a pair of 

 short siphons ; in Cypricardia, according to Mr. Woodward's description 

 of C. Solenoides, the lobes are united, with only moderate openings for the 

 foot and siphonal orifices, while in Cardita the lobes are described by M. 

 Deshayes as being entirely disunited and having consequently no siphonal 

 tubes. The probability is that the animal varies in these respects even in 

 the same genus, according to the nature of its habitat, the species living in 

 stone-borings having a less-developed foot and a more closed-up mantle 

 than the free-living species. 



Cypricardia. Cardita. Cardium. Isocardia. 



Genus 1. CYPRICARDIA, Lamarck. 



Animal ; {of C. Solenoides) ivith mantle-lobes united, cirrated be- 

 hind ; pedal opening moderate ; foot small, compressed, with a 

 large byssalpore near the heel ; siphons short, conical, unequal, 

 cirrated externally ; orifices fringed. (Woodward.) 



Shell ; equivalve, very inequilateral, elongately ovate, never ribbed, 

 anterior side very short, posterior mostly angled ; hinge com- 

 posed of three short teeth beneath the umbo of each valve, and 

 a single elongated, rather remote, lateral tooth, which is some- 

 times nearly obsolete. 



The Cypricardia produce an oblong, smooth or concentrically fimbriated, 

 shell of a peculiar opake white substance, delicately and variously tinted 

 with purple, rose, or orange ; and the animal of C. Guinaica, collected by 



