DONAX. 337 



rather broad, conspicuous white ray runs from the beaks, 

 with but very trifling obhquity, to the commencement of 

 the posterior third of the ventral margin. This latter is 

 comparatively straight, the anterior portion bending but 

 little from its regular curve, and ascending with a moderate 

 upward inclination to the well-rounded anterior extremity. 

 The dorsal edges are tolerably straight, the front is but 

 little, and the hinder but very moderately sloping. Hence 

 the posterior wedge-shaped termination is very blunt, the 

 tip being rather broad and well-rounded. As the umbonal 

 ridge is rather obscure, the hinder area is not distinctly 

 defined ; it is not, however, flattened, and the lips pout, 

 or project outwards. The sides for a Donaso are not pe- 

 culiarly unequal, the anterior one not being quite double 

 the length of the other. The ligament is short, promi- 

 nent, and of a rich fulvous brown ; the lunule is very in- 

 distinctly impressed. The beaks, which are by no means 

 prominent, are yet sufficiently acute at their apices, which 

 are scarcely inclined, and are sometimes purple, sometimes 

 orange yellow, and sometimes white. One of the more 

 beautiful varieties has the umbonal region of a deep violet, 

 with the beaks of a snowy whiteness. The interior of the 

 shell, which has its margins simple and not creuated, is 

 usually of a rich purple or violet ; sometimes, however, it 

 is white, somewhat radiatingly stained with purple, and 

 the vicinity of the beaks adorned with a deep and brilliant 

 orange. The hinge of the right valve presents the ordi- 

 nary solid bifid hinder primary tooth, and the very oblique 

 and almost linear front one, with a rudimentary linear in- 

 termediate one (to be met with in many, if not most of 

 this genus) ; in the right valve, in addition to the diver- 

 gent narrow almost simple primary teeth, are two small 

 approximate sublateral ones, of which the anterior is so 



