BIVALVES DONAX. 37 



DONAX. Wedge-shell. 



DESCRIPTION OF PLATE IX. • 



Div. I.— Fig. 1. D. scortum. 

 DiY. II.— Fig. 4.. D. denticulata. Drv. Ill— Fig. 3. D. madagascariensis. 

 Fig. 5. D. trunculus. Div. IV. — Fig. 2. D. scripts. 

 Fig. 6. D. elongata. Fig. 7> D. stultonun. 



Shell bivalve, with generally a crenulated margin, the frontal margin 

 very obtuse; hinge with two teeth, and a single marginal one 

 placed a little behind, rarely double or triple. 



THE principal characteristic of the Donax is deriv- 

 ed from its form, which (throughout its twenty-four 

 species) is similar to that of a wedge, being very broad 

 and thick at one extremity, and gradually tapering to- 

 wards the other. The margin, which is generally of a 

 deep color, is almost invariably crenulated or beset 

 Avith small contiguous teeth ; and the frontal margin is 

 generally very obtuse: the anterior slope not unfre- 

 quently gapes, and has a ligament situated near the 

 fissure, which prevents the two valves from sepa- 

 rating, when the animal has occasion to open them. 



Some specimens of this genus, in their external ap- 

 pearance, bear a strong resemblance to the species of the 

 Venus ; but the examination of the hinge will always 

 determine to which of the genera the shell belongs. 



The Donax presents so great a diversity in external 

 character, that it has occasioned the genus to be sepa- 

 rated into five divisions. In the first, the species ex- 

 hibit a rough and decussated surface, caused by crowd- 



