CHAPTER XXVIII : THE WING SHELLS, PEARL 

 OYSTERS AND HAMMER OYSTERS 



Family Aviculid/e 



Shell oblique, valves unequal, right one smaller, always 

 underneath; hinge line straight, much elongated; umbones 

 eared, one ear wing-like; animal attached bybyssus; foot small; 

 mantle lobes fringed, free. Family mostly extinct; one thousand 

 fossil species known, chiefly in Paleozoic strata. Of one hundred 

 and twenty living species, not one is found in northern latitudes 

 where fossils abound. Confined now to warm, temperate and 

 tropical seas. 



Genus AVICULA, Lam. 



Shell oval, eared, posterior ear produced into a wing-like 

 extension. Body small; byssus large. Many species secrete 

 pearls. Twenty-five living and three hundred fossil species. 

 The typical forms resemble in outline the profile of a bird in flight. 



The Saffron Wing Shell (A. crocea, Lam.) has a long, 

 slender wing-like extension of the hinge, almost twice the length 

 of the oblique valves. The short anterior wing completes the 

 bird figure, supplying the head and beak. This was Lamarck's 

 type species. Who wonders that he called the genus Avicula — 

 "little bird"? The trim outline of this elegant shell is that of 

 a swallow, built for swift flight. Length, 4 to 5 inches. 



Habitat. — Philippines. 



A. heteroptera, Lam., has roundish, unequal valves, and 

 long, tapering, dissimilar wings. Colour, bright chestnut, ob- 

 scurely rayed. Length, 3 to 4 inches. 



Habitat. — New Holland. 



The Great-winged Avicula (A. macroptera, Lam.) com^ 

 bines unusual size with elegance of form. The straight, narrow 

 wings extend like keen stillettos in opposite directions from the 

 central hinge. The dusky valves are thin and marked with pale 



393 



