THE 



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Genus Corbula. The valves of this shell are very unequal, and produced behind; they do not 

 gape ; the right valve, which is the largest, has a prominent tooth in front of the cartilage pit ; 



the smaller left valve has projecting 

 processes ; the siphons of the animal 

 are short and united, the foot is 

 pointed. There are sixty species liv- 

 ing. It inhabits the lower lamination 

 zone, and dwells in eighty fathoms. 



ANATOMY OF SOFT PARTS OF MVA AREXAHIA. 



Genus Thetis. This shell is nearly 

 circular; the umbones are prominent; 

 the valves are translucent and in- 

 flated ; the interior is slightly pearly; 

 there are one or two hinge teeth ; 

 the ligament is external; the pallial 



<r, the Anterior, and a', the Posterior Abductor Muscle ; ex, the Excurrent, and in, the Inrurrent line Simple. FlV6 Species are found 



Siphon ; g g, the Gills, or Branchia; f, the Foot ; , the Labial, or Lip-tentacles; o, the Oral ,. . -y-, . . .-, T ,. . 



Aperture, or Mouth; s, the Stomach; a, the Intestine opening into the Excurrent Siphon; JlVinff in .Britain, r ranee, Lndia, (fee. 

 p, the Pedal, or Foot, Muscle; m, the Mantle. ' 



Genus Panopcea. In tins genus 



the valves are equal ; they are thick, more or less oblong, and open at either end ; the hinge ligament 

 is external ; there is a prominent tooth in each valve ; the siphonal indentation is deep. This is an 

 Arctic form, extending from the White Sea to Norway and Britain. The Panopseas are great 

 buvrowers; they dwell from low water to 100 fathoms. The shell attains a length of six or 

 eight inches. Eleven species are found living in the North Sea, Mediterranean, &c. 



Some of the British shells fetch high prices on account of their rarity, although their appearance 

 is by no means attractive. The rude-looking bivalve called Panopcea norvegica cannot be obtained for 

 less than three guineas ; and there is an unusually good specimen in the collection of Mrs. Pe Burgh, 

 which was offered to the British Museum for six guineas and declined, but afterwards realised nearly 

 that amount. Tellina balaustina is a much smaller but brightly-tinted shell, of which there is 

 a specimen in the British Museum worth three guineas. 



FAMILY XXI. ANATIKID^E. 



The Anatinidce have thin, nacreous, inequivalve shells, with an external ligament and an 

 internal cartilage ; the siphons are long and united ; the gills are single on each side. A large 

 proportion of this family only occurs fossil. 



Genus Anatina, "Lantern-shell." The hinge is provided with a spoon-shaped cartilage 

 process in each valve ; the siphons are long, united, covered with wrinkled epidermis ; there is one gill 

 on each side ; the foot is very small. Fifty species are found living in India, West Africa, the 

 Philippines, and New Zealand. 



Genus Thracia. Thracia jmbescens and Anatina subrostrata, and its sub-genus Periploma 

 prcetenue, are all closely allied forms of the family Anatinidce. There are seventeen species of Thracia, 

 extending from Greenland to the Canaries and China, living at a depth of from four to 120 fathoms. 



Genus Pholadomya. The shell is transversely oblong, equivalve, thin, white, and translucent, 

 gaping at both ends, pearly inside ; the surface of the valves is ornamented with radiating ribs. 

 Although 160 species are known fossil, only one recent form is known, which is occasionally met 

 with on the shores of the Island of Tortola, in the West Indies, after hurricanes, being probably 

 thrown up from deep water by the force of wind and waves. 



Genus Lyomia. The valves of this shell are thin, somewhat pearly, the left being a 

 trifle the larger ; the posterior end is truncated ; the cartilage plates are oblique ; the animal has 

 a tongue-shaped foot, which is grooved, and spins a byssus. Twelve species are known, ranging from 

 Greenland to Madeira and the Indian seas. 



Genus Pandora. This genus has thin, closely- fitting valves, pearly inside ; the right valve 

 is flat, with a diverging ridge and cartilage ; the left valve is deep, with two diverging grooves 

 at the hinge ; the foot is narrow, and the siphons very short. Eighteen species are known living, 

 ranging from Spitzbergen to Panama, India, &c. 

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