ACEPHALA TESTACEA. 269 



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, Petricolae, &c. They are much sought for on 

 account of their agreeable flavour. 



TEREDO, Linnaeus. 



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

 valves, and terminated by two short tubes, the base of which is furnished on 

 each side with a stony and moveable kind of operculum or palette. These 

 Acephala, while quite young, penetrate and establish their habitations in sub- 

 merged 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 

 effected, and through which, by the aid of its palette, it receives water and 

 aliment. The gallery it inhabits is lined with a calcareous crust 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 seaports of Europe. 



Teredo navalis, Lin. 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, Bruguieres. 



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

 and is more or less like a bottle or club. The Fistulanae are sometimes found 

 buried in submerged fragments of wood or in fruits, and the animal, like 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 



GASTROCH.ENA, Spengler, 



Where the shells are deprived of teeth, and their edges being wide apart ante- 

 riorly, leave a large oblique opening, opposite to which there is a small hole in 

 the mantle for the passage of the foot. The double tube, which can be retraced 

 completely within the shell, is susceptible of being greatly elongated. It appears 

 that they are certainly furnished with a calcareous tube. 



They inhabit the interior of Madrepores, which they perforate. 



Two genera of Acephala furnished with tubes, have been detected among 

 fossils, but the first of them, the 



TEREDINA, Lamarck, 



Has a little hollow on the inside of each of its valves, and a small, free, shield- 

 shaped piece on the hinge. In the second, the 



