HALF AN HOUR WITH SHELL-FISH (BIVALVES). 225 



Fig. 125. 



Pectunculus glycimeris. 



empty shells of other molluscs. Perhaps one of the 

 most striking of all our native bivalves is one that 

 is common on our southern coasts, although less 

 plentiful elsewhere, called Peetunculns glycimeris 

 (Fig. 125). It is two inches across, nearly round in 

 shape, having numerous strong 

 hinge-teeth, which radiate from 

 each side the centre. The 

 exterior is covered with fine 

 lines running down to the mar- 

 gin, and over all there is a 

 series of zig-zag, red mark- 

 ings, which produce a very 

 pretty effect. It is on the 

 southern coasts also, and we 

 believe there alone, that we obtain the Pinna, the 

 largest of British bivalves, as it sometimes attains 

 the length of twelve inches, anchoring itself by means 

 of a long silken byssus. Mr. Couch says that these 

 beautiful shells, off the Cornish coast, " stud the bottom 

 in multitudes, with only two or three inches of the 

 pointed end inserted in the mud." One end of the 

 shells the broad end cannot be closed by art ; but 

 Mr. Couch, quoting Montagu, the celebrated con- 

 chologist, says of it : " The animal is capable of 

 effecting it, and observation has taught me that this 

 is its method of obtaining food. In its ordinary 

 position this opening is about two inches wide, 

 exposing the contained animal, which occupies but 

 a small portion of the cavity, and seems to offer 



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