Ill 



taining the body of the animal, is obliquely attached to 

 a long, straight, transverse base, and resembles a bird's 

 wing; the two extremities of the base (which are fre- 

 quently elongated and of unequal length), may be 

 compared to the tail ; so that the shell when but par- 

 tially expanded, presents the appearance of a bird fly- 

 ing, from which fanciful resemblance Lamarck has de- 

 rived the name of this genus. Shell inequivalve, with 

 a sinus or singular notch in the left valve, through 

 which the byssus passes: hinge linear, with one pri- 

 mary tooth on each valve, beneath the apices, which 

 are oblique, small, and not projecting. The shell 

 is generally thin and very fragile, the interior part 

 pearly in the centre, with a broad black border sur- 

 rounding it, and the margin terminated in a fringe oc- 

 casioned by the epidermis or foliaceous texture of the 

 exterior. — Sowerby has united this genus with the 

 following. 



Avicula macroptera 



lotorium 



semi-sagitta 



heteroptera 



falcata 



crocea 



Avicula virens. 

 [There are also two fossil species.] 



Avicula Tarentina 



Atlantica 



squamulosa 



papilionacea 



costellata 



physoides 



