48 BIVALVES. DONAX. 



the other. The frontal margin is generally very obtuse, and 

 the anterior slope is not unfrequently furnished with a sort 

 of fissure or gape ; near to which is situated a cartilaginous 

 ligature or ligament, which prevents the two shells from 

 separating when the animal has occasion to open them. 



Some of this genus, however, are a little ambiguous in 

 their external appearance ; so much so, that they frequent- 

 ly create a doubt whether they should not be ranked among 

 the species of the Venus; but in these cases the hinge alone 

 must be the guide, which in the Donax is furnished with 

 two teeth, and a single marginal one placed a little behind, 

 not often double or triple. 



The exterior of the Donax is generally of a smoothish 

 surface, though many are covered with nearly obsolete lon- 

 gitudinal striae, being embellished at the same time with 

 numerous reddish or purple rays, diverging from the beaks 

 to the margin. Other species are perfectly rough on their 

 outside, which is caused by crowded striae crossing each other 

 in a longitudinal and transverse direction ; this disposition 

 of the striae gives the shell a foliated and even a spiny ap- 

 pearance, as in the D. scortum and D. pubescens. 



A very prevalent colour in this genus is a fine rich pur- 

 ple or purple rays on a white ground ; many of the species, 

 however, are of an olive-yellow cast, which not unfrequent- 

 ly inclines to a bright orange; others, again, have a pink 

 hue, and are finely lettered with brown zigzag markings, 

 as the D scripta, &c. and in some instances the shells have 

 a banded appearance. The interior almost always par- 

 takes of the colouring of the exterior; and the margin, which 

 is generally of a high colour, is almost invariably crenulat- 

 ed or beset with small contiguous teeth. 



The species and varieties of this genus are but few, and 

 thinly scattered over most parts of the globe ; yet some 

 coasts (the European in particular) supply a profusion, but 



