Heart-Cockle and Fresh-water Cockle 1 1 5 



forepart is swollen, and the upper part above tlie 

 beaks compressed. Greenish yellow is the colour of 

 the shell, which is covered by a thin, brown, glossy 

 epidermis. The lines of growth are strongly marked, 

 and the interior is white with a pearly iridescence. 

 The animal is grey, tinged w^ith red or yellow ; the 

 large foot yellow or orange ; the edges of the mantle 

 tinsfed with brown and frino^ed. It occurs in slow 

 waters and ponds almost throughout Britain, usually 

 in large colonies. It is calculated that full-grown 

 specimens are twelve or fourteen years old. The 

 Duck Mussel {A. anatina) 

 is considered by many 

 conchologists to be merely 

 a variety of A. cygnea. 

 There can be no doubt that 

 it is very closely related 

 to it, and probably arose 

 quite recently as a variety, 

 but it appears to be now a 

 permanent form, and per- 

 haps would be more cor- 

 rectly described as a sub-species of A. cygnea. 

 The shell is proportionately longer, and less swollen, 

 of thicker material, olive or brown in colour, with 

 darker concentric bands, and w4th green rays from 

 the beaks. The hinge-line is slightly curved, and 

 higher than in A. cygnea. The animal differs from 

 its congener chiefly in the larger size of the lower 

 siphon, which is also fringed with more numerous 

 and more delicate tentacles. It is found in similar 

 situations to the last, but is not so widely distributed, 

 and does not appear to occur in Ireland. 



