ACEPHALA TESTACEA. 381 



properly so called, a lamina projecting from one vaive into tne other, and an internal ligament proceeding 

 from that lamina to a corresponding fossa. The cloak is reflected outward upon the hinge, and con- 

 tains one or sometimes two or three supernumerary pieces. The foot issues by the opening at the side 

 of the mouth, which is the widest, and from the opposite end there comes out the two tubes united in 

 one, and capable of being extended in every direction. The Pholades inhabit cells which they have 

 made, some in the mud, others in rocks, [and others in wood]. They are sought after [in some 

 countries] from their agreeable taste. 



P/iolas dactylus, Linn., occurs on our coasts. [The g-enus Xylophaga of Turton, which burrows in decayed wood, 

 is reduced by Deshayes to Pholas.] 



The Teredines {Teredo, Linn.) — 



Have 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 \\\i\\ a calcareous and moveable kind 

 of operculum or palette. These Acephales, while quite young, penetrate and establish their habitations 

 in submerged pieces of wood, such as piles, ship's 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 Uned 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. 



The common species (T. navalis, Linn.), which is said to have been introduced from the torrid zone, has more than 

 once threatened Holland with ruin, by the destruction of its dikes. It is six inches in leng^th and upwards, and 

 has simple palattes. In tropical countries, there are large species with jointed and ciliated palettes, which desen'e 

 notice for the analogy they establish with the Cirrhopodes. Such is the Teredo palmulalus, Lam. 



The Fistulana, Brug. — 

 Has been distinguished from Teredo, for its external tube is entirely closed at its larger end, and is more 

 or less like a bottle or club. The species are sometimes found buried in wood or fruits that have been 

 apparently submerged in the water ; sometimes they are simply enveloped in the sand. The animal 

 has twro small valves and two palettes, as in the Teredo. Recent specimens are brought from the 

 Indian Ocean, but our formations have preserved some fossil species. 



Near Fistulana we should place Gastrochccna, Spengler*, whose shells have a toothless hinge, and the margins 

 being nide apart in front, leave a large oblique opening, opposite to which there is in the cloak a small opening for 

 the passage of the foot. The double tube, which can be concealed entirely within the shell, is capable of great 

 elongation. It appears certain that they have a calcareous tube. In some species, the beaks are at the anterior 

 angle; in others, near the middle. They live in the interior of madrepores, which they perforate. ["This bivalve 

 is inclosed in the posterior clavate extremity of a shelly tube, which is attenuated and open anteriorly, its aperture 

 being oblong and bilobate, or nearly divided into two by a sort of septum which does not quite meet in the centre: 

 this double aperture serves for the passage of the two tubes of the animal : the posterior extremity of the shelly 

 tube is closed. This irregular clavate tube, already inclosing the two valves of the Gastrochaena, is generally found 

 within some other shell, to the inside of which it is attached, or it is protected In the ready-formed cavities of shells 

 or rocks, or it lines cavities perforated by the animal itself in rocks, shells, or corals, and in this latter case, the 

 double termination of the shelly tube projects beyond the surface of the coral or other object in which it is 

 inclosed."] 



Among fossils, two genera have been recognized furnished with tubes like the Teredo, but the first [Teredina, 

 Lam.] has a little, spoon-shaped cavity in each valve, and a little loose piece, in form of a shield, at the hinge. 

 The other (Clavagella, Lam.) has one of its valves agglutinated to the tube, and the other loose. A living species 

 is found in the madrepores of the Sicilian seas, which has been described by M. Audouin. [The best description 

 of this genus is given by Messrs. Broderip and Owen in the Trans, of the Zoological Society.'] 



Some naturalists think we should also place in this family 



The Aspergillum, — 



The shell of which is formed of an elon- 

 gated, conical tube, closed at its widest ex- 

 Vi^^l^^ trcmity by a disk perforated with numerous 

 "*'t~f ?>ma\\ tubular holes ; the httle tubes of the 

 ■ 'j^ outer range, being longest, form a kind of 

 corolla round it. Tiie reason for approxi- 

 mating them to tlie Acephala with tul)es is 



F,B 193 -Aspergillum. f^jj^j j„ ^,^g f.^^^ ^^^^ ^^^^.^ j^ ^ ^j^^^j^j^ 



• According lo Deshnyes, rinslrociieena and Fistulana are tlie same.— Ed. 



