424 MOLLUSCA. 



trate and establish their habitations in submerged pieces of wood, 

 such as piles, ships' bottoms, Sec, perforating and destroying them 

 in every direction. It is thought, that in order to penetrate as fast 

 as it increases in size, the Pholas excavates the wood by means of 

 its valves; but the tubes remain near the opening by which its en- 

 trance was effected, and through which, by the aid of its palette, it 

 receives water and aliment. The galle^-y 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 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. 

 Larger species inhabit hot countries, whose palettes are articu- 

 lated and ciliate. They should be remarked for their analogy to the 

 Cirrhopoda. Such is the Teredo palmulatus, Lam., Adans., Ac. 

 des Sc, 1759, pi. 9, f. 12. 



FisTULANA, Brug. 



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

 larger end, and is more or less like a bottle or club. The Fistula- 

 nae are sometimes found buried in submerged fragments of wood or 

 in fruits, and the animal, like 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( 1). We should 

 approximate to them the 



Gastroch^na, Spengler. 



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

 apart anteriorly, leave a large oblique opening, opposite to which 

 there is a small hole in the mantle for a passage of the foot. The 

 double tube, which can be retracted completely within the shell, is 



(1) Teredo dava, Gmel., Spengl., Naturforsch., XIII, 1 and 2, copied Encyc. 

 Method., Vers., pi. clxvii, f. 6 — 16. It is the Fistulana gregata. Lam.; — Teredo 

 utriculus, Gm., Naturf., X, i, 10; probably the same as the Fistulana lagenulay 

 Lam., Encyc, Method., I, c, f. 23; — Fistulana dava, Lam., lb., IT, 22. 



It is probable that the Pholas teredula. Pall., Nov. Act. Petrop., II, vi, 25, is also 

 a Fistulana. 



