372 



Ethekiid^.- 



-JIOLLUSCA.- 



-LlTHODOMUS. 



six hundred tliousand young sliells. This genus is 

 lepreseuted in Pkite 11, fig. 13, by Anodonta cygnea. 



Family— ETHERIIDjE. 



The Etherias have the shell irregular in shape, in- 

 eqnivalve, covered externally with a thick olive epider- 

 mis, and pearly within. The outer surface of the valves 

 is very uneven, and frequently beset with tubular pro- 

 cesses, while the internal surface is blistered, as if with 

 air-bubbles, leaving cavities in the form of small vesi- 

 cles, or very thin bladders between the plates. The 

 hinge is without teeth, and the ligament subinternal. 

 The adult shells are always attached to each other, or 

 to foreign bodies, by the outer surface of one of the 

 valves; but when young is free, like Anodon. In this 

 young state the animal, as Dr. Gray observes, may 

 possess a foot, but being adherent when adult, this 

 organ becomes unnecessary. The little cavities in the 

 inner substance of the shell, are believed to be filled 

 with water when the animals are alive. 



Gknus Etiieria. — This genus adheres by the beak. 

 The species are all natives of fresh water, being chiefly 

 found in the river Nile, above the Cataracts, and in 

 the river Senegal. Bruce, in his "Travels," mentions 

 tliese shells under the name of " fresh-water oysters." 

 Tliey are collected, he informs us, by the natives as 

 articles of food, and the shells are employed by them 

 for ornamenting their tombs. For a representation of 

 the family, see Plate 11, fig. 16 — Etiieria cailtaudii. 



Family— MYTILIDiE. 



The Mussels secrete a byssus. The shell is equi- 

 valve, elongated, closed, with the beaks anterior. The 

 valves are covered externally with a dark thick epi- 

 dermis, and they are more or less pearly within. The 

 hinge is witliout teeth, and the ligament is internal, 

 Bubmarginal, and very long. 



Genus Mytilus, the Sea Mussel — This genus has a 

 wedge-shaped shell, rounded behind, and the beaks ter- 

 minal and pointed. The species of Mytili are nunjerous, 

 and are world-wide in their distribution. The byssus 

 which the animal spins is strong and coarse, and these 

 shells are usually found attached to rocks, stones, float- 

 ing bodies, &c. It appears, however, from the observa- 

 tions of Dr. Gould of Boston, that mussels are not quite 

 stationary animals, but that they can move from place 

 to place with great facility. The manner in which the 

 common edible mussel, Mytilus edulis, forms its con- 

 nection with the rocks and stones, &c., is explained by 

 Beauraur. By placing some individuals in a vase of 

 sea-water, he was able to watch the process. " Opening 

 their valves, the foot was first protruded, and with 

 various strains and stretches, gradually thrust out, 

 until at length the elongation was carried to the de- 

 sired extent, sometimes to fully two inclies. It was 

 now employed in feeling or testing all the objects 

 within reach, directed to the right or left, or backwards 

 or forwards. After all this prelude, to ascertain ap- 

 parently the security of the intended holdings, the 

 point of the foot is settled and retained for a short time 

 on the chosen spot, when again, it is suddenly removed, 



and immediately withdrawn entirely within the shell, 

 leaving behind a thread that reaches from the spot to 

 the base of the foot. By many repetitions of this 

 operation, carried on patiently day after day (for not 

 above four or five threads are spun in the twenty-four 

 hours), and by attaching the disc-like extremities of 

 the threads to different places, the mussel at last com- 

 pletes its cable, and secures a safe anchorage." 



Mussels are also used as bait for fishes, and as food 

 for man. 



THE EDIBLE MUSSEL {M. edulis, Plate 11, fig. 17) 

 freqnents mud banks, which are uncovered at low water, 

 are very prolific, and attain their full growth in a single 

 year. They abound in a great many parts of our coasts, 

 and immense quantities are yearly consumed. Their 

 fisliery occupies a considerable number of persons, espe- 

 cially where the mussels have obtained a reputation for 

 superior excellence. "This is the case with the mus- 

 sels of Buddie Bay, on the coast of Northumberland ; 

 and those of Isigny, near Bayeux, and of other places 

 on the western coast of France, are held in high esti- 

 mation. Mussels, however, of inferior delicacy are 

 found in very great abundance on the rocks which 

 border the coast between St. Malo and Cancale, in the 

 department De la Manche, where they are torn from 

 their attachments by means of an iron hook at low 

 water ; and the annual profit of this fishery is estimated 

 at from 2000 to 2500 hunvs."— (Johnston.) The con- 

 sumption of mussels in Edinburgh and Leith is estimated 

 at four hundred bushels {^= four hundred tliousand 

 mussels) annually; enormous quantities, Mr. Woodward 

 informs us on the authority of Dr. Knapp, are also used 

 for bait, especially in the deep-sea fishery, for which 

 purpose tliirty or forty millions are collected yearly in 

 the Firth of Forth alone. It is a curious fact that of 

 all edible moUusks, the common mussel is that which 

 proves most frequently poisonous to those who eat 

 them. Dr. Johnston says that he has known them to 

 produce an itchy eruption and swelling over the whole 

 body, attended with great anxiety and considerable 

 fever. Many instances of their having proved dele- 

 terious are mentioned in this author's excellent " Intio- 

 duction to Conchology," and amongst otliers one that 

 occurred in 1827 in Leith, which I well remember as 

 having produced a great sensation in that town and 

 in Edinburgh. Two or three deaths look place, and 

 upwards of thirty people were severely afi'ected. The 

 cause of this unwholesomeness of mussels, at certain 

 seasons, is still a matter of conjecture. 



Genus Modiola or Horse-Mussel. — This genus 

 has an oblong shell, inflated in front, and the beaks 

 obtuse and placed a little behind the extremity. The 

 species of Modiola are numerous — about seventy hav- 

 ing been enumerated. They are chiefly tropical in 

 their distribution, though a few are found in the Medi- 

 terranean, Great Britain, and even in the Arctic seas. 

 They differ chiefly from the Mytili in the position of 

 the beaks, and in their habit of burrowing or spinning 

 a kind of nest in which they occasionally conceal them- 

 selveo. They range from low water to an hundred 

 fathoms. 



Genus Litiiodomus. — The Date shells have a 

 cyliudrioally oblong shell, rounded and inflated in front, 



