282 MOLLUSCA. 



three teeth in each valve near the anterior extremity, where the foot issues. 

 The latter is conical, and enables the animal to bury itself in the sand, 

 which it excavates with considerable rapidity on the approach of danger. 



Pholas, Lin. 



The Pholades have two broad valves, convex towards the mouth, narrow 

 and elongated on the opposite side, and leaving a large oblique opening at 

 each extremity; their hinge, hke that of a true Mya, is furnished with a 

 plate projecting from one valve into the other, and with an internal hgament 

 running from that plate into a corresponding cavity. Their mantle is re- 

 flected externally upon the hinge, where it sometimes contains two or three 

 supernumerary calcareous bodies. The foot issues through the aperture 

 on the side next to the mouth, where it is widest, and from the opposite one 

 project the two tubes, which are united and susceptible of inflation in every 

 direction. 



The Pholades inhabit canals which they excavate, some in ooze and others 

 in stone, like the Lithodomi, Petricolse, &c. They are much sought for on 

 account of their agreeable flavour. 



Teredo, Lin. 

 The mantle extended in a tube much longer than the two small, rhomboi- 

 dal valves, and terminated by two short tubes, the base of which is furnish- 

 ed on each side with a stony and movable kind of operculum or palette. 

 These Acephala, while quite young, penetrate and establish their habita- 

 tions in submerged pieces of wood, such as piles, ships' bottoms, &c., 

 perforating and destroying them in every direction. It is thought, that 

 in order to penetrate as fast as it increases in size, the Teredo excavates the 

 wood by means of its valves? but the tubes remain near the opening by 

 which its entrance was eff"ected, and through which, by the aid of its pa- 

 lette, it receives water and aUment. The gallery it inhabits is lined with a 

 calcareous ci-ust which exudes from its body, and which forms a second 

 kind of tubular shell for it. It is a noxious and destructive animal in the 

 sea ports of Europe. 



Teredo navalis, L. This species, which is the most common, and is said 

 to have been introduced into Europe from the torrid zone, has more than 

 once threatened Holland with ruin by the destruction of its dikes. It is 

 upwards of six inches in length and has simple palettes. 



FisTULANA, Brug. 



Separated from Teredo; the external tube is entirely closed at its larger 

 end, and is more or less hke a bottle or club. The Fistulanae are some- 

 times found buried in submerged fragments of wood or in fruits, and the 

 animal, hke that of a Teredo, has two small valves, and as many palettes. 

 Recent specimens are only obtained from' the Indian Ocean, but they are 

 found fossil in Europe. We should approximate to them the 



