112 



MELEAGRINA. 



MYTILUS MARGARITIFERUS. — Llfltl. 



Sowerbys Genera, No. 14, yl. 4. 

 A very great affinity exists between this genus and the 

 preceding, from which, however, it is distinguished by 

 being equivalve, always without the elongated trans- 

 verse base, or the cardinal tooth, and by the form of the 

 shell, which is orbicular, and frequently eight inches in 

 diameter: in addition to these distinctions, the sloping 

 sides of the opening, admitting the passage of the byssus, 

 is perceptible on both valves, which is never the case 

 with the G. Avicula, where a notch answers the same 

 purpose: the exterior of the valves is less smooth, and 

 generally covered with scales. Hinge linear and with- 

 out teeth, their substance solid, very thick, and of a bril- . 

 liant pearly appearance, from which many elegant trin- 

 kets are made: and the extravasation of the liquor des- 

 tined to the periodical augmentation of the shell, pro- 

 duces those isolated deposits of nacreous matter called 

 pearls, the finest of which are found in the Meleagrina 

 margaritifera, the type of this genus, commonly called 

 the mother-of-pearl oyster. Sowerby has united it with 

 the Avicula; and mentions the existence of some fossil 

 species in the London clay, and strata identical with it. 

 Meleagrina margaritifera Meleagrina albina. 



