82 CONCHIFERA. MONOMYAIRA. 



Gen. 22. MELEAGRIMA, Lam. Mytilus, Lin. 

 Shell subequivalve, rounded, scaly without ; a sinus at the pos- 

 terior base of the valves for the passage of the byssus, the 

 left valve being notched and narrow at this place ; hinge li- 

 near, without teeth ; ligament marginal, elongated, almost 

 exterior, dilated in the middle. 



The nacreous portion of the shell of this genus is sometimes very thick and bril- 

 liant; and the extravasation of the fluid destined for the interior augmentation of 

 the shell often gives rise to isolated depositions of this beautiful substance, which is 

 known in commerce by the name of pearls. This genus is not numerous in spe- 

 cies ; but the best known one is celebrated as affording the finest pearls. The shell 

 itself, when deprived of its outer covering, is the mother of pearl of artists. 



M. margaritifera, Lam. (M. margaritiferus, Lin.) Shell sub- 

 orbicular, compressed, covered with transverse membranaceous 

 scales ; inside pearly ; colour greenish or pale chestnut, with pal- 

 er rays. 10 or 12 inches long, full grown shells. Inhabits In- 

 dian seas. D'Argenv. pi. 20, fig. A. 



M. albina, Lam. Shell white, shining, obsoletely squamose, with 

 two distinct ears. 2^ inches long. Inhabits seas of New Hol- 

 land Lam. vi. 1, 152. 



Gen. 23. AVICULA, Lam. Mytilus, Lin. 

 Shell inequivalve, fragile, with the base transversal, straight, 

 the extremities projecting, and the anterior caudiform ; a 

 notch on the left valve ; hinge linear, with a single tooth in 

 each valve under the beaks ; ligament linear, external. 



The shells of this genus are marine, almost always smooth without, and in gene- 

 ral thin, fragile, and pearly in the inside. The principal part of the shell rises ob- 

 liquely in a form approaching to that of the wing of a bird from the base, and the 

 two extremities of this base are often prolonged but unequal, one of them repre- 

 senting a taiL The beaks are oblique, small, and not projecting. 



A. macroptera, Lam. Shell large, blackish exteriorly ; wing large, 

 obliquely curved ; tail pretty long. Inhabits the seas of warm 

 climates Lam. vi. 1, 147- 



A. semisagitta, Lam. Shell black or reddish yellow; wing oblique, 

 subventricose ; tail long. Indian seas. Lister, pi. 220, fig. 55. 



A. Tarentina, Lam. Shell slender, fragile, grayish, radiated with 

 brown ; wings broad ; valves equal. Inhabits the Mediterranean 

 sea. Lam. vi. 1, 148. 



Gen. 24. MALLEUS, Lam. Ostrea, Lin. 

 Shell subequivalve, rugged, distorted, often elongated, sublobed 

 at the base ; beaks small, diverging ; hinge without teeth ; 

 an elongated conical furrow under the beaks ; ligament ex- 

 terior, inserted on the slope of the valves. 



The singular forms of some species of this genus render them very remarkable. 

 They have a transverse lobe on each side of the hinge, and the general shape of the 

 shell resembles the letter T ; hence the popular name of the Hammer Oyster which has 

 been applied to them. There is nothing agreeable in their exterior, though the 

 place which the body of the animal occupies is often brilliant pearly. 



