ACEPIIALA TESTACEA. 373 



adlipre to all sorts of bodies, [and tlieir form is generally modified by the surface of the objects on ^vhich 

 they grow]. 



M. de Laciiarck separates from the Spondylus his Plirafula, from havinj? no external area, or disk, between the 

 beaks ; and flat, almost equal, irregular, plaited and scalv valves, as in many Oysters. {Sp. jylicalus, Gmeh, is the 

 type.] 



Malleus, Lam. — 

 lias a simple fossa for the ligament, as in Ostrea, with which genus Linnreus 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 hin^e extended 

 so as to1"orm somethin^^ like the head of a hammer, while the valves, elonicated in a traiisverHe direction, represent 

 the handle. It iidiabits the Archipelai^^o of India. Other species, which are, perhaps, hut the young of the Malleus, 

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



Vulsella, Lara. — 



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

 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. Tlie shell is elongated ia a direction perpen- 

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



Perna, Brug. — 

 lias across the hinge several parallel fossa3 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. Linnaeus left them also 

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



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

 broad hin^^e, have Httle oval ones quite on the margin, where they occupy httle breadth. It does not appear that 

 there is any byssus. We find them often buried in spong^es. To the PeruEe, it is supposed, we must approximate 

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

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

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

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

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

 mandy.] The Inoceramtts, 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 Cafilles, Brongn., have, independently of 

 fossie, 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 librous texture. They appear to have had a byssus. The Pul- 

 vinites, Defr., have a triangular regular shell, and its fossae, 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 w^hicb follow, besides the 



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



Yalve 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 iEtheria and Ostrea, and as apparently connecting the regular freshwater bivalves 



with the irregular marine bivalves (Ostrcie), and with the genus /Etberia, inasmuch as in the sinus at 



the posterior extremity of the ligament it resembles the Naiades and the jEtherias ; 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 Ostreae 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, E-rug. — • 

 \ las 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 



