364 



Div. 2. MOLLUSCA.— ACEPHALES. 



Class 4. 



observable in the two valves.] The large species of our coasts {Ostrea maxima, Linn.), is the Pil^im's shell, [worn 

 in front of the hat by those who had visited the shrine of St. James in the Holy Land.] It is eaten. 



The Liniffi {Lima, Bru"-.) differ from the Pectens in havins? a more elongated shell, with shorter ears, and a 

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

 living state, and the cloak is ornamented with a vast number of filaments of different lengths, without tubercles ; 

 and further within there is a broad fold which closes the gape of the 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 white colour (Ostrea Lima, Linn.), is eaten. 



Pedum, Brug. — 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 

 tcntacula. Its byssus is larger. The one species known is from the Indian sea. 



Certain fossils may be placed here which have the hinge, ligament, and central muscle of the Ostreae, Pectines, 

 and Limae, but are distinguished by some peculiarities of the shell. The Hitutites, Defr., seem to be (Jysters, or 

 Clams, with small ears and adherent shells, irreguhar and very thick, especially the convex valve, lliere is a fossa 

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

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

 without scales, and the outlet of the byssus less. They are found in formations older than the chalk. Tlie 

 Pachytes, Defr., have nearly the figure of the Pectines, a regular shell with small ears ; there is a transverse flat 

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

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

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

 opercula : 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 Blainville regards the preceding four genera as nearer allied to Tere- 

 bratula; and M. Deshayes, on the contrary, approximates them to Spondylus.) 



Although multivalve, we should approximate 



The Anomi.e, Brug., — 

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

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

 that of the Ostrea. The greater part of the central muscle traverses this 

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

 sometimes horny, by which the animal adheres to foreign bodies ; and the 

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

 {Echion, Poli) has a small vestige of a foot, similar to that of a Pccteii, 

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

 perhaps serves to direct water to the mouth, which is adjacent. Their 

 shells are found attached to various bodies, like Oysters. They are found 

 in every sea. 



[Placunomia, Sowerby, is the link which connects Anomia with the following genus. AVith an arrangement of the 

 hinge, approaching very nearly to tliat of Placuna, we have the distinguishing organization of Anomia, while the 

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

 Bome of the plicated Oysters. The organ of adhesion resembles that of Anomia, but is inserted between the lamina: 

 of the internal surface of the lower valve, above the muscular impression, and below the hinge, and passes out into 

 an external, irregular, somewhat longitudinal superficial fissure, or cicatrix, narrowest at the hinge margin, and 

 which it entirely fills to a level with the surrounding surface of the shell. Three species are known, natives of 

 the tjopical seas.] 



The iVacj/zirt, Brug., is aflined to the Anomiw, and, like them, have thin, unequal, and often irregular valves, 

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

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



Spondylus, Linn. 



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

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

 fossae in the opposite valve respectivciy : the two middle teeth belong to the most convex valve, which 

 is usually the left, and has, behind the hinge, a projecting flattish beak, as if it had been sawed. Like 

 the Pectines, the margins of the cloak of the animal .-J^'c garnished with two rows of tcntacula, and in 

 the outer row there are several terminated with coloured tubercles : in front of the abdomen is a vestige 

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

 elongation. From its centre there hangs a thread terminated with an oval mass, the use of which is 

 unknown. The Spondvli are eaten like Oysters. Their sliclls are very often vividly coloured. Tlicy 



fig. ISC. — .\nomia Cjilrpiiium 



