AVICULA. 251 



AVICULA. Lamarck. 



Shell oblique, inequivalve, inequilateral, upper valve 

 most convex, lower one notched for the passage of the 

 byssus ; surface smooth, or scaly, or radiatingly ribbed ; 

 hinge-line straight, often winged ; a single cardinal tooth 

 in each valve ; ligament partially external, linear. Pallial 

 impression entire; muscular scars two or more, one very 

 large, the rest small. 



Animal shaped like the shell, its mantle freely open, 

 with cirrhated margins ; no siphons ; foot small, cylindric, 

 furnished with a byssal groove ; palps large ; adductor 

 muscles very unequal, one being greatly larger than the 

 rest. 



Although during ancient epochs sufficiently plentiful in 

 the seas of our area, now we have but one species of 

 this genus, and that one exceedingly rare. Its living 

 allies are for the most part tropical, and some of them 

 grow to a great size, and are remarkable for beauty 

 or eccentricity of shape, or for the pearls they furnish; 

 for Meleagrina, from species of which the best pearls are 

 fished in the Indian Seas, is at best but a subgenus of 

 Avicula. 



A. Tarentina, Lamarck. 



Plate XLII. fig. 1, 2, 3, and (Animal) plate S. fig. 4. 



Mijtilus hirundo, Linn. Syst. Nat. ed. 12, p. 1159 (partly). — Turt. Conch. Dic- 

 tion, p. 109, f. 7 — PoLi, Test. Sicil. vol. ii. p. 221, pi. 32, f. 

 17 to 21.— Dill w. Recent Shells, vol. i. p. 321 (var. G.).— 

 Mawe, Introd. Linn. Conch, pi. 16, f. 6.— Costa, Cat. Test. 

 Sicil. p. 59. 

 „ e mari Mediterratieo, Chemn. Conch. Cab. vol. viii. p. 142, pi. 81, f. 725. 



Avicula hirundo, Ti7rt. Dithyra Brit. p. 220, pi. 16, f. 3,4. — Flem. Brit. Anim. 

 p. 405.— Brit. Mar. Conch, p. 113. 



