BIVALVE SHELLS. 39 



Genus 16.— M YTILUS. 



Animal allied to an Ascidia ; shell bivalve, rough, generally 

 affixed to other bodies by a byssus or beard of silky filaments ; 

 hinge mostly without teeth, having a subulate, excavated, 

 longitudinal line. Plate VII. fig. 16. 



The Linnean Mytili are divided into three families : * parasitical, aflBxed as 

 it were by claws, as exemplified in the Mytilus Crista Galli ; ** flat or com- 

 pressed into a flattened form, and slighted eared ; as in the r.Iytilus Mar- 

 garitiferus ; *** elongated, ventricose, or convex, as in Mytilus Edulis. 



Mytilus edulis. — The Edible Muscle. Plate 11. fig. 4. and 

 6. Shell oblong, pointed at the beak, sides much sloped ; an- 

 terior side a little angulated ; smooth, and radiated with deep 

 blue or purple ; covered with an umber coloured epidermis. 

 Inside, round the margin, of a fine blue, which grows gradually 

 lighter towards the centre; cicatrix very distinct and glossy; 

 i)eneath the beak are several crenulations, which some have 

 supposed to be teeth. 



This is the most common shell we have, and well known by 

 the name of muscle. It forms a pleasant and nutritious food. 

 They have, however, in some localities proved poisonous, and 

 fatal consequences have followed eating them. The true nature 

 of this poison has not yet been satisfactorily accounted for. 



Plate II. fig-. 4- and 6. a The cartilage, v v length of the shell, u u breadtli 

 Oi the shell, o disk, ?• r the beak. 



Mytilus Incurvatus. — The Incurvated Mytilus. Plate 

 VII. fig. 16. Oblong oval, nearly smooth, both valves much 

 inflated, and curved on one side near the ligament, apex acute, 

 and base much widened. Inhabits the British coasts. Pro- 

 bably it is only a variety of the Mytilus edulis. 



It is to the Mytilus Margaritiferus, (the Meleagrina margaritifera of 

 Lamarck,) Plate X. fig. 10. that we are indebted for that precious gem, the 

 real pearl. It is an inhabitant of the Indian ocean ; where it is regularly 

 fished for by men who dive to the bottom of the sea, in places where it fre- 

 <;ueuts. lu this p.'riluas employment, the divers are often attacked by 

 Kharks, and not unfrequently lose their lives.— Mother of pearl ornaments 

 are made from the shell itself. 



The Mytili inhabit the ocean, lakes, rivers and ponds. Marine muscles 

 sdhere to rocks or beds by a thin but very tenaceous byssus, consisting of 

 extremely fine and tough filaments, and some to the Gorgoniae by claws. 

 Some penetrate calcareous and argilaceous rocks, where they reside without 

 <lianging place, others adhere to rocks or clay on the shore. They are much 

 used for bait or food, and as such they are esteemed by many. The fresh 

 water muscles are generally found on the surface, or a little way under the 

 mud. M'ist species of muscles produce pearls, 



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