38 BIVALVES. — DONAXr 



the other. The frontal margin is generally very obliise, 

 and the anterior slope is not unfrequently furnished with 

 a sort of fissure or gape; near to which is situated a carti- 

 laginous 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 fre- 

 quently hold forth an inducement to rank them 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 some- 

 what behind, not often doubled or tripled. 



The exterior of the Donax is mostly of a smoothish sur- 

 face, though many are covered with nearly obsolete lon- 

 gitudinal striee, 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 cross- 

 ing each other in a longitudinal and transverse direc- 

 tion; this disposition of the striae gives the shell a fo- 

 liated and even a spiny appearance, as in the Donax 

 scortum and pubescens. 



A very prevalent color in this genus is a fine rich 

 purple, or purple rays on a white ground ; however, many 

 of the species are of an olive-yellow cast, which not un- 

 frequently inclines to a bright orange; others, again, 

 have a pink hue, and are finely lettered with brown zig- 

 zag markings, as is the case in the Donax scripta, &c. and 

 in some instances the shells have a banded appearance. 

 The interior almost always partakes of the coloring of 

 the exterior; and the margin, which is generally of a 

 high color, is almost invariably crcnulatc or beset ^"s ith 



