372 



MOLLUSCA. 



ODservable in the two valves.] Tlie lar^e species of our coasts [Odrea maxhna, Linn.), is tbe Pi i2:rin-i's shell, [worn 

 in front of tlie liiit by those who had visited the shrine of St. James in the Holy Laml.] It is eaten. 



The Lima:' {Lima, BruK-) differ from the Pectens In havino; a more elon;;ate(l shell, with shorter ears, and a 

 greater inequality of the sides. The majority liave the ribs raised into scales. The valves cannot be closed in the 

 liviiiii; state, and the cloak is ornamented with avast number of filaments of different lerif^^ths, without tubercles ; 

 and further within thei'e is a broad fold which closes the gapeoftlic shell, and even forms a protuberant veil. The 

 foot is small, and the byssus inconsiderable. The Lima; swim rapidly, by flapping their valves. One species in 

 the Mediterranean, of a pure wliite colour {Ostrea Lima, Linn.), is eaten. 



Pedum, Brus;'. — The shell is similar to Lima, but the valves are unequal, and the most convex only has a deep 

 sinus for the byssus. The animal also Is very like that of Lima, but its cloak has only a single row of small slender 

 tentacula. Its byssus is laricer. The oni' spi-cies ku'nvn is from the Indian sea. 



Certain fossils may be placed here vvliich have Mie bins^e, lig'ament, and central muscle of the Ostrese, Pectines, 

 and Limai, but are distint^-uished by some peculiaiities of the shell. The Hiimi/es, Defr., seem to be (!)ysters, or 

 Clams, with small ears and adherent shells, irreg^ular and very thick, especially the conve.x valve. There is a fossa 

 at the hinge for the ligament. (Four recent species of this genus have been described.) The Plagiostome-fy Sower., 

 have the oblique shell of the Linue, flattened on one side, very minute ears, the valves more ventricose, striated, 

 ^vithout scales, and the outli4 of the byssus less. They are found in formations older than the chalk. Tlie 

 P,irhi/fcs\ DeiV., have nearly the figure of the Pectines, a regular shell with small ears ; there is a transverse flat 

 spnce between their summits, which has a strong triangular emargination in one of the valves, tlirough or in which 

 the ligament passes or is lodged. The Dianchores, Sower., have unequal oblique valves, one of them adherent and 

 perforated in the summit, the other free and eared. The Podopsides, Lam., have regular striated valves, without 

 Ojiercula : one has the apex more prominent than the other, truncated and adherent ; this apex is often very thick, 

 and forms a kind of stalk to the shell. (M. de RIainville regards the preceding four genera as nearer allied to Tere- 

 bratuia; and M. Oi.-shayes, uii the contrary, appruxiinates them to Spondylus.) 



Although niultivalve, we should apiiroximate 



Tr-iE Anomi.^, Briig., — 

 To tlie Oysters. They have two thin, unequal, irregular valves, the flattest 

 of wliich is deeply notched on the side of the ligament, which is similar to 

 that of the 0;5trca. The greater part of the central muscle traverses this 

 opening, to be inserted into a third plate, that is snuietimes calcareous and 

 sometimes horny, hy which the animal adlieres to foreign hodie> ; and the 

 remainder of the muscle serves to join one valve to the other. The animal 

 [Ediiijii, Poll) has a small vestige of a foot, similar to that of a Pccten, 

 which glides between the emargination and the plate that closes it, and 

 perhaps serves to direct water to the month, which is adjacent. Tlieir 

 shells are found attached to various hodies, like 0\sters. They are found 

 Fig. 186.— ADomia eijiiippiom in cvcry sca. 



[Plucunomia, Sowerby, is tlie link which connects Anomia with the following genus. "With an arrangement of the 

 hinge, approaching very nearly to that of Placuna, we have the distinguishing organization of Anomia, ^vljile the 

 external appearance of the shell, especially if viewed in water, bears the strongest resemblance to a Plicatula, or 

 some of the plicated Oysters. The organ of adhesion resembles that of Anomia, but is inserted between the laminrc 

 of the intei-nai surface of the lower valve, above the muscular impression, and below the hinge, and passes out into 

 an external, irregular, somewhat longitudinal suiierlicial tissure, or cicatrix, narrowest at the hinge margin, and 

 \sliirh it entiiely fdls to a level with the surrounding surface of the shell. Three species are known, natives of 

 thr trnpicfd seas,] 



'I'he /-'/'^(■(//^'(, Brug., is allineil to the Aimmi.'e, anil, like thcin, have thin, unequal, and often irregular valves, 

 but neither are perforated. On one of tliese valves, near the hinge, we perceive two pruniineut ribs, forming a 

 triangle whose apex is towards the hinge. The animal remains unknown. 



SeoNDYLUs, Linn. 

 Tliese have a rough and foliated shell, like the Oysters, and frequently spiny, hut their hinge is more 

 complicated, for, besides the fossa for the ligament, there are two teeth in each valve tliat enter into 

 fuss;e in the opposite valve respecti\('Iy ; the two middle teeth belong to the most convex valve, which 

 is usually tlie left, and has, behind the hinge, a ])rojectiiig flattish heak, as if it had been sawed. Like 

 the ['cctiiies, liie margins of the cloak of the animal are garnished with two rows of tentacula, and in 

 the outer row there are several terminated with coloured tubercles : in front of the alidouien is a \estigc 

 of a foot, under the guise of a Ijroad radiated disk with a short pedicle, and capable of contraction and 

 elongatiun- Fiuiu its centre there hangs a thread terminated with an oval mass, the use of wdiich is 

 unknown. The Spond^li are eaten like Oysters. Their shells are very often vividly coloured. Tiicy 



