ACEPIIALA TESTACEA. 373 



adhere to all sorts of bodies, [and their form is generally modified by the surface of the objects on which 

 they grow]. 



M. de Lamarck separates from the Spondylus his Plicafiila, from having; no external area, or disk, between the 

 beaks ; and flat, almost equal, irreg;ular, plaited and scaly valves, as in many Oysters. [Sp. plicatus, Gniel., is the 

 type.] 



Malleus, Lam. — 

 Has a simple fossa for the ligament, as in Ostrea, with which genus Linnaeus left this one, and the more 

 so as the shell is also inequivalve and irregular, but it is distinguished by an emargination on the side 

 of the ligament for the passage of a byssus. 



The best known species (Ostrea malleus, Linn.), a rare and dear shell, has the two sides of the hinge extended 

 so as to form something like the head of a hammer, while the valves, elongated in a transverse direction, represent 

 the handle. It inhabits the Archipelago of India. Other species, which are, perhaps, but the young of the Malleus, 

 have no hammer-head, and these we must be careful not to confound with the Vulsellae. 



Vulsella, Lam. — 

 Has in the hinge, on each side, a little lamina projecting inwards, and it is from one of these lamin;c 

 that the ligament, similar in other respects to that of the Oyster, is stretched to the other. On the 

 side of the lamina is a sinus for the egress of the byssus. The shell is elongated in a direction perpen- 

 dicular to the hinge. The species best known inhabits the Indian Ocean. 



Perna, Brug. — 

 Has across the hinge several parallel fossae opposed to each other in the two valves, and lodging as many 

 elastic ligaments : their shell is irregular and foliated, like the Oysters, and has on the anterior side, 

 underneath the hinge, an emargination, through which the byssus passes. Linusus left them also 

 among his Ostres. [The recent species are brought from the Indian Ocean, and from New Holland,] 



Tliere has been recently separated from Perna, the Crenatidce, Lam., which, instead of transverse fossae on a 

 broad hinge, have little oval ones quite on the margin, where they occupy little breadth. It does not appear that 

 there is any byssus. We find them often buried in sponges. To the Perna;, it is supposed, we must approximate 

 some fossils which have more or less numerous fossae in the hinge answering to one another, and appearing also 

 to have given attatchment to ligaments. Thus the Gervillia;, Defr., have a shell almost similar to Vulsella, but 

 with a hinge in some degree double; the exterior with opposed fossas receiving as many ligaments, and the interior 

 garnished with very oblique teeth on each valve. We find the casts of them with Ammonites in compact limestone. 

 [Many species have occurred at various geological periods from the lias upward, to the baculite limestone of Nor- 

 mandy.] The Inoceramus, Sower., is remarkable for the elevation and inequality of the valves, of which the 

 summit is hooked near the hinge, and whose texture is lamellated. The Catilles, Brongn., have, independently of 

 fossae, for the ligament, a conical furrow drawn in a varix, which is bent at a right angle to form one of the margins 

 of the shell. The valves are nearly equal, and of a fibrous texture. They appear to have had a byssus. The Pid- 

 vhiites, Defr., have a triangular regular shell, and its fossas, few in number, diverge within from the summit. 

 Their casts are found in chalk. 



The second subdivision of the Ostracea, as well as almost all the bivalves which follow, besides the 

 single transverse [or adductor] muscle of the preceding genera, have another muscle going from one 

 valve to the other, and placed in front of the mouth. It is apparently in this subdivision that we must 

 place 



[The Mulleria, De Fer., — 

 One of the most singular and rare of known genera. It is remarkable as being intermediate in its 

 structure between /Etheria and Ostrea, and as apparently connecting the j-egular freshwater bivalves 

 with the irregular marine bivalves (Ostreae), and with the genus yEtheria, inasmuch as in the sinus at 

 the posterior extremity of the ligament it resembles the Naiades and the iEtheriae ; and in its single 

 muscular impression, as well as its general form, it approaches to Ostrea.] 



Etheri.«, Lam. — 

 Are large inequivalved shells, as, or even more, irregular than the Oysters, without teeth to the hinge, 

 and where the ligament, in part external, exists also interiorly. They differ from the Ostrea; in having 

 two muscular impressions. It is not ascertained that their animal produces a byssus. They have lately 

 been discovered in the Upper Nile. 



AvicuLA, Brug. — 

 Has a shell with equal valves, and a rectilinear hinge, often extended into wings on each side, furnished 

 with a narrow, elongated ligament, and sometimes with small denticulations on that side which is next 



