241 



PECTINID.E. 



PECTINID^E. 



242 



longitudinal and angulated ; internal border rough ; externally violet, 

 purplish, or reddish-white. The shell externally has aubgranulous 

 striae, and subtubular scales. It is found in the East Indian Seas. 



The number of recent species of Ostrea is 60, and of fossil 200. 

 (Woodward.) 



Placuna (Brug.). Animal very much compressed. Shell free, 

 irregular, very much flattened ; valves delicate and almost translucid, 

 quite translucid in some species, nearly equal, and subequilateral ; 

 hinge internal, offering on one valve two longitudinal, trenchant, rib- 

 like elevations, converging at the summit, and on the other two 

 furrows, corresponding to those ribs, and giving attachment to the 

 ligament ; muscular impression subcentral and rather small. (Rang.) 



The species now known are from the East Indian and Red Seas, 

 and have been taken on sandy bottoms. 



M. Desbayes remarks that the animal is not known, but that he is 

 convinced that it has a great analogy to that of Anomia. 



The number of species recorded in the list of M. Deshayes is three 

 living and one fossil (tertiary). Of the living species, P. papyracea 

 . is noted as both living and fossil (tertiary). Four species are enume- 

 rated in the last edition of Lamarck as they were in the first ; but 

 the fourth, P. pcctinoida (fossil), is considered to have all the cha- 

 racters of Plicatula, and is therefore removed by M. Deshayes to that 

 genus. Mr. G. B. Sowerby had previously given a similar opinion. 

 The species best known are, P. Placenta, vulgarly known as the 

 Chinese Window-Oyster, the valves of which are sufficiently delicate 

 to transmit light ; and P. Sella, known to collectors as the Saddle- 

 Oyster (from Tranqucbar, &c.). 



P. Placenta has the shell suborbicular, flat, pellucid, white, with 

 longitudinal subdecussate stria;. It is found in the East Indian Seas. 



Pl.cuna riaceiita. 



Anomia (Brug.). Animal very much compressed, having the borders 

 f the mantle delicate, and furnished externally with a row of tentacu- 



filaments. Foot rudimentary ; adductor muscle divided into three 



inches, tha largest of which passes by a notch in the lower valve in 

 order to attach itself to an opercular stony or corneous piece fixed to 

 marine bodies. Shell adherent by its opercular piece, inequivalve, 

 inequilateral, irregular, delicate, and often translucid; the fixed valve 

 most flattened, having a round or oblong notch near the umbo for the 

 reception of the opercular piece ; the other larger and more concave ; 

 both joined by a short and thick ligament ; muscular impression sepa- 

 rated into three portions. (Rang.) 



HAT. nut. niv. VOL. iv. 



The recorded species are generally quoted as coming from the 

 European seas and the Atlantic Ocean. The depths at which they 

 have been taken are stated to vary from the surface to 100 fathoms, 

 adhering to oysters, and other shells, rocks, &c. 



The species are not very numerous; and perhaps more are recorded 

 than actually exist ; for the shell will take upon itself the regularities 

 or irregularities of the body to which it is attached. Thus, on a 

 Pecten, an individual will become striated like that Pecten through 

 both valves, when another of ,the same species is smooth if adherent 

 to a comparatively smooth body. M. Rang observed this frequently 

 on the shores of the Mediterranean ; and both Mr. G. B. Sowerby and 

 M. Deshayes make the same observation. 



There are 20 recent and 30 fossil species. The fossils are found 

 in the Crag and London Clay, in the marine formations above the 

 Chalk in France, and as low down as the Oolite. 



A. Ephippium. Shell suborbiculate, rugoso-plicato, waved, planu- 

 late, with an oval foramen, whitish or yellowish, often reddish-yellow, 

 below. One of the largest species. It is found in the British Channel, 

 the Mediterranean Sea, and Atlantic Ocean. 



Anomia Ephippium. 



a, valves closed ; J>, open to show the hinge ; e, hinge of attached valve with- 

 out the bony appendage. 



a 



Bony appendage of Anomia Ephippium adhering to the rock. 

 a, the bony part that goes through the opening of the shell ; b, the surface 

 which is attached to external objects. 



M. De Blainville records a species, Anomia iquamata, which has not 

 this bony appendage, and which he says is affixed by the valve itself. 

 This so-called species, however, which should be Squamula, is in Mr. 

 G. B. Sowerby's opinion nothing more than A. Ephippium. in a very 

 young state before the appendage is ossified. 



Anomia iffuamata. 



Placunanomia of Broderip has the following generic character : 

 Animal probably intermediate between that of Placuna and Anomia. 

 Shell adherent, subequivalve, irregular, flattened, plaited towards 

 the margin, vitreous internally. Hinge internal, with two elongated, 

 thick, subcurved, divaricated teeth converging at the base in the lower 

 valve, and two h'gamentiferous furrows opposite in the upper valve. 

 Lower valve superficially fissured externally towards the hinge, the 

 subosseous organ of adhesion inserted between the lamina; of the 

 shell, and filling the fissure externally. Muscular impression in each 

 valve subcentral. In the upper valve the impression of the organ of 

 adhesion is superadded. 



This sub-genus partakes of the characters of the genera Ostrea, 

 Plicatula, Placuna, and Anomia. It may be regarded as the con- 

 necting link between the two latter. With an arrangement of the 

 hinge approaching very nearly to that of Placuna, it has the dis- 

 tinguishing organisation of Anomia, while the external appearance of 

 the shell, especially if viewed in situ, bears the strongest resemblance 

 to Plicatula, or some of the plicated Oysters. The organ of adheaiou, 

 which in its bony character (for it is more bony than shelly) resembles 

 that of Anomia, does not perforate tha lower valve directly, but is 

 inserted between the lamina; of the internal surface of the lower 

 valve above the muscular impression and below the hinge, and 



B 



