40: BIVALVES. DONAX. 



hinge alone must be the guide, which in the Donax is 

 furnished with two teeth, and a single marginal one plac- 

 ed 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 

 longitudinal 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 cross- 

 ing each other in a longitudinal and transverse direction ; 

 this disposition of the striae gives the shell a foliated and 

 even a spiny appearance, as in the D. scortum and D. 

 pubescens. 



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

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

 cies, however, 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 zigzag 

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

 the shells have a banded appearance. The interior al- 

 most always partakes of the coloring of the exterior; 

 and the margin, which is generally of a high color, is al- 

 most invariably crenulated or beset with small contigu- 

 ous teeth. 



The species and varieties of this genus are but few, 

 and thmly scattered over most parts of the globe; yet 

 some coasts (the European in particular) supply a profu- 

 sion, but of no great variety; they are usually found bu- 

 ried in the sand. It is not exactly ascertained whether 

 any of this genus are natives of rivers. 



The Donax derives its name from its shape, which re- 

 sembles the barbed head of a javelin or dart. 



