CARDIACE.E. SOLENIDJE ; RAZOR-SHELL. 413 



means by which they make their excavations, are not understood. 

 The resemblance both in the shell and the animal, among these 

 numerous genera, is often so strong, as to produce a difficulty in 

 their classification, as well as to render it unnecessary to enter 

 here into details respecting them. It will be sufficient to name 

 the genera, Venus, Mactra, Tellina, Donax, Lucina, Petricola, 

 and Venerupis, as including the greatest proportion of the group ; 

 these being names with which even the ordinary Shell-Collector 

 must soon become familiar, on account of the large proportion 

 that the bivalves of this Order bear to others, on almost every 

 coast. 



ORDER IX. SOLENID^E. 



956. The Mollusks of this Order are distinguished from those 

 of the preceding, by the wide gape of their shells at the poste- 

 rior extremity, and by the length of the respiratory tubes. Their 

 habit is to burrow much more deeply ; and their foot (which is 

 of small size) is made to project rather from the anterior 

 extremity, than from the middle of the body ; so that the form 

 of the whole is more cylindrical than we have yet seen it, though 

 not so much so as in the succeeding Order. The Solen^ or Razor- 

 shell, is a well-known example. of this group. It has an elongated 



11, of which the hinge is furnished with distinct teeth, and the 

 ligament is altogether external* The animal burrows in the 

 sand, into which it sinks rapidly on the approach of danger". It 

 seldom or never quits its hole ; and its movements are nearly 

 limited, therefore, to an ascent or descent in it. This it 

 accomplishes by means of its foot, which it elongates and 

 attenuates into a point, when it wishes to bore ; contracting 

 it into a rounded form, so as to fix it by its enlargement within 

 the hole, when it desires to rise. The animal is sought for by 

 fishermen on some coasts, as a bait for certain fish. Its burrow 

 is often recognised by the little jet of water which the animal 

 throws out, when alarmed by the shaking of the sand occasioned 

 by the motion of the fisherman above. When the tide is low, 



