130 GASTROCH^NIDiE. 



tube sometimes protects the valves, ami in certain genera 

 unites with tliem. These tubes are very regular and curious 

 in some of the exotic species, especially in those which live 

 buried in sand. This habit is not merely the living habitu- 

 ally and freely in sand, as the razor fish do, but rather 

 the treating of it in the manner of a substance bored into, 

 and the tubes are to be regarded as the linings of the 

 perforations so made. All the species of the family are 

 borers, most of them preferring calcareous rock. 



GASTROCH^NA, Spengler. 



Shell cuneiform, equivalve, widely gaping, valves very 

 inequilateral ; hinge simple, linear, toothless, but furnished 

 with a small spathulate lamina ; ligament external, long ; 

 muscular impressions small, distant, connected by a slightly- 

 marked, sinuated, palleal impression. 



Tube calcareous, claviform, free or fixed, often incom- 

 plete. 



Animal cuneiform, or when the siphons, which are sepa- 

 rate only at their extremities, are extended, elongated ; 

 orifices fringed ; mantle closed, and thickened when ex- 

 posed ; with a very small opening for the small, pointed, 

 curved, finger-shaped foot, which sometimes spins a delicate 

 byssus. Mouth with two equal, simple lips, and a pair of 

 sickle-shaped labial tentacula. 



This genus is chiefly interesting on account of the curious 

 tubes which are formed by the several species, often en- 

 veloping them in the manner of a flask. M. Deshayes be- 

 lieves* that the animal, at certain periods, can dissolve a 

 part of its tube, and so enlarge its capacity, observing with 



• Mollusijues d'Algeric, p. 24. 



