THE PEARL OYSTER. 909 



is reserved for those in which the auricles are more pointed 

 and the shell is more oblique ; they have on the hinge 

 before the ligament the vestige of a tooth at least, of 

 which scarcely any trace is perceptible on the Pintadines. 



As the two so-called genera thus stand, it may be 

 convenient to consider them separately, under a family 

 title ; for even if it be deemed unphilosophical to retain the 

 two genera, still Avicula seems to be the type of a family 

 form. 



THE BROAD-WINGED AVICULA. 



(Avicula macroptera). This shell, when the valves 

 are represented open so as to display the hinge, will con- 

 vey a better idea of the general characteristics of the genus 

 than any verbal details. These shells, as those also of the 

 genus Meleagrina, are natives of the warmer seas, where 

 they moor themselves at various depths to the surface of 

 rocks, old shells, and other submarine objects. 



THE PEARL OYSTER. 



(Meleagrina Margaritifera.) Mytilus Margaritiferus, 

 Linnaeus ; Avicula Margaritifera, Sowerby. 



The young of this interesting shell are marked with 

 beautiful foliations, which disappear when the shell has 

 attained to a large size. 



The valves are semicircular, greenish externally, and 

 lined internally with a layer of the most beautiful nacre. 



The foot in this tribe is small, and produces a byssus, 

 by which the animal attaches itself firmly to submarine 

 objects. The mantle lobes are free, the shell usually 

 oblique and somewhat triangular, with the valves unequal, 

 and the hinge usually without teeth. The ears are com- 



<~* j 



paratively small ; that is, in comparison with others of the 

 Aviculaceae. 



