CONCHOLOGY. "79 



A. maa-optera. The rounded Avicula. PI. 14, fig. 3. 

 Species oval, oblique, the earlike appendages very de- 

 veloped, especially the superior ; one tooth at the hinge. 



A. Atlantica. The Atlantic Avicula. 

 Obliquely curved, yellowish fawn colour, with dark red- 

 dish-brown stains ; interior pearly. 



5. Meleagrina. Two species. 



The form of the shell is orbicular and equivalve, without 

 the elongated transverse base on the cardinal tooth, and the 

 sloping sides of the opening for the passage of the byssus 

 are perceptible on both valves ; these peculiarities distin- 

 guish it from the Avicula. 



Shell sub-equivalve, rotundate, nearly square, externally 

 squamose ; the inferior cardinal margin straight, not caudate 

 anteriorly ; a sinus at the posterior base of the valves for 

 the passage of the byssus ; the left valve being at this place 

 narrow and channelled ; hinge linear, without teelh. 

 Meleagrina margaritifera. Meleagrina albina. 



M. margaritifera. The pearl-bearing Meleagrina, some- 

 limes called the mother-of-pearl oyster. 



Species slightly oblique, somewhat square, pearly, very 

 thick, compressed ; undulated and transversely striated, with 

 a series of lamellated longitudinal scales ; exterior greenish, 

 interior pearly. This shell is celebrated for its irridescent 

 colours, and is valued for the beautiful and costly pearls it 

 produces. These pearls are formed from a deposition of the 

 substance destined to line the shell upon sand or other bod- 

 ies, casually or purposely introduced within the mantle of 

 the animal ; the shell itself is the mother-of-pearl used for in- 

 laying, or making various elegant trinkets. 



