O^t-s hells and Aiussels 65 



as a Tertiary fossil, in a living or recent state it is 

 rare. A few specimens have been taken in deep 

 water (85 fathoms) off the Shetlands. It is a very 

 small, glossy white shell, marked with fine lines 

 radiating from the beak, and crossed by irregular 

 ridges. The yellow-brown epidermis takes the form 

 of a frino^e of lono^ hairs. The margins of the shell 

 are rounded except behind the hinge, where its 

 straightness gives the eared appearance to the shell. 

 Like those of the Doo'-Cockle, the strong^ teeth of 

 this species are in a continuous line, but confined to 

 the hinge - plate. The lower margins are devoid of 

 teeth. It has a long thin foot, by means of which it 

 creeps and climbs, and spins an almost transparent 

 thread. 



The Common Mussel (Mytilus ediilis) is one of the 

 most useful of the Mollusca to mankind, for in 

 addition to its wide use as a food, it is of great value 

 as a bait in the long-line fishing. Strongly gregarious 

 in its habits, it attaches itself to rocks, timbers, and 

 masonry by its tough byssus spun by the short dark- 

 brown foot. This habit of associating in closely 

 packed masses has doubtless led to the contracted 

 wedgelike form of the shell, and to the absence 

 of — in this case — unnecessary hinge or marginal 

 teeth. Occasionally a few small hinge - teeth are 

 developed, but as the species indulges in very little 

 locomotion after early life these are not much needed. 

 The mantle has a double margin, the outer one plain, 

 whilst the inner is at different parts fringed or 

 toothed, and on the hinder part formed into an im- 

 perfect siphon. 



Though the Mussel is always found hung up by its 



