ACKi^lJALxl TESTACl^A. 381 



properly so called, a lamina projecting from one Yaive 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 month, which is the widest, and from the opposite end there comes out the two tnltes united in 

 one, and capable of l)cing extended in every directimt. Tiie 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 agreealile taste. 



Pholas (lactiilus, Linn., occurs on our coasts. [The penus Xylophagn of Turton, which burrows in decayed wood, 

 is reduced by Dcsliayes to Photas.] 



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 with 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 iu 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 ahment. The gallery it 

 inhabits is lined with a calcareous crust which exudes from its body, and which forms a second kind 

 of tubular sliell for it. It is a noxious and destructive animal in the seaports of Europe. 



The common epecies (T. jiat-alis, Linn.), which is said to have lieen introduced from the torrid zone, has more than 

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

 has simple palattes. In tropical countries, there arelarg"e species with jointed and ciliated palettes, whicli deserve 

 notice for the analog^y they establish with the Cirrhopodes. Such is the Teredo palmidaius. Lam. 



The Fistulana, Brug. — 

 lias 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 tw^o small valves and two palettes, as in the Teredo. Recent specimens are brought from the 

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



Near Fistulana we should place Gastrochixna, Speu^fler*, whose shells have a toothless hinf|;e, and the margins 

 bciu.^ wide apart in front, leave a larg'e oblique opening, opposite to which there is in the cloak a small opening- for 

 tlie piissaf::;e of the foot. The double tube, which can be concealed entirely within the shell, is capable of p:reat 

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

 ang-le; in others, near the middle. They live in the interior of madrepores, which they perforate. ["Thisbivalve 

 is inclosed in the posterior clavate extremity of a sliellytube, 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 npertnre serves for the passage of the two tubes of the animal : the posterior extremity of tlie shelly 

 tube is closed. This irregular clavate tube, already iuclosiitgthe two valves of the Gastrocha;na, is generally found 

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

 or lockfi, or it lines cavities pei-foi-ated by the animal itself in rocks, shells, or corals, and in this latter case, tlie 

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

 inclosed."] 



Among fossils, two genera have been recognized furnished with tubes like the Teredo, but the first [Te?Trf(»rt, 

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

 Tlie otlier (C/avafjella, 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. Autlouin. [The best description 

 of this genus is g-iven by iNIessrs. Broderip and Owen in the Trans, of the Zoological >Jocie/i/.] 



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- 

 tremity by a disk perforated with numerous 

 small tubular holes ; the little tubes of the 

 outer range, being longest, form a kind of 

 corolla round it. The reason for approxi- 

 mating them to the Acephala with tubes is 



F,E !93-A.pcrBilluni. fQ^„^^| J,^ ^j^^ f^^j. ^^^^ ^j^^^.^ .^ ^ doublc 



• AccorJing lo Deshavcs, Gaslrucneeiia ami fiatiUana ure iIjc iamc— Eo 



