GASTROCilyENA. 



side, wlien viewed in front, and acuminated posteriorly ; 

 the anterior side gapes very widely, its aperture being 

 rather oval, hut pointed behind; the hinge is linear and 

 marginal, and the ligament external, but we do not find 

 any hinge teeth: there is, indeed, a small and indistinct 

 laminated appendage which proceeds from within the 

 limbo, and which Turton has described as a tooth, but we 

 think it should rather be likened to the long curved 

 appendage of Pholas than to the hinge teeth of bivalves 

 in general. This bivalve is enclosed in the posterior, 

 clavate extremity of a shelly tube, which is attenuated 

 and open anteriorly, its aperture being oblong, and bilo- 

 bate or nearly divided into two by a sort of septum which 

 does not quite meet in the center; this double aperture 

 serves for the passage of the two tubes of the animal: the 

 posterior ej^tremity of the shelly tube is closed. This 

 irregular clavate tube, already enclosing 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 enclosed: we have an Oyster 

 shell in which about a dozen of them have taken up their 

 abode, whose shelly tubes project more or less beyond the 

 surface, but generally in those situations in which they 

 are protected by the irregularities of the Oyster shell. 



The Mya dubia of Pennant, and the Pholas hians of 

 Chemn. may be considered as the types of this Genus, they 

 are both recent shells, and the former is found on our 

 coasts; we are only acquainted with one fossil species 

 which is frequently found attached to the insides of many 

 of the Grignon shells. Gastrocha3na is easily distinguished 

 from Pholas, by its shelly tube, its ligament by which the 

 two valves are attached^ and its wanting the accessory 

 valves. 



Fig. 1. A group of tlie tubes of Gastr. modlolina, Lam. one of which being 

 broken shows the two valves in situ, from the Mediterranean. 



2. A specimen of Fusus Nose, from Grignon, cut open to show the cla\'ate 

 tube of a little fossil Gastrochaena. 



3. A worn fragment of a Madrepore, broken to show the tube formed by 

 a specimen of Gastrochaena cuneiformis. Lam. 



4 & 5. Two views of the two valves of G. cuneiformis, Lam. 



