TilE NAUTILUS. 125 



It must not be confounded with U. Hazelharstianus Lea, which 

 has a rougher, blackish epidermis, greater breadth and not so in- 

 flated. 



We take pleasure in naming this species for the discoveror, ]Mr. 

 Oscar B. Webster, of Lake Helen, Florida. 



ON THE SPECIES OF DONAX OF EASTERN NORTH AMERICA. 



BV W. H. DALL. 



Genus Donax Linne. 



The name Donax is derived according to most authorities from a 

 Greek word meaning a reed or pole, perhaps in allusion to the 

 radiating striae which might recall a tuft of reeds. This word is 

 derived from the feminine verb doneo, to wave or shake, and the 

 author of the genus has regarded the resulting noun as feminine, 

 forming the terminations of his adjective specific names in a. Some 

 later authors have taken the derivative Latin Donax a reed, or, 

 secondarily, a slender fish (Pliny), as the original form and have 

 regarded the word as masculine. It would seem best to fellow the 

 original usage. In the endeavor to identify some species of this 

 genus from the Tertiaries of North Carolina it has been necessary 

 to revieAV the recent species of the genus from the eastern coast of 

 the United States and the result may be summarized in the follow- 

 ing table. 



Donax s. s, 



A. With a distinctly sculptured lunule. 



a. Strise punctate, lunule smaller than the truncation. 



D. clenticulata Linne. Texas, Bahamas, West Indies to Rio Janeiro, 



b. Strise simple, lunule co-extensive with truncation. 

 D. rugosa Linne. Extra-limital, West Indies to Rio. 



B. Without lunule, strise simple. 

 1. Sharply truncate. 



a. Riblets of the truncate area simple. 

 Z>. striata Linne. Extra-limital, Antilles, Colon. 

 D. Roemeri Phil. Short, triangular. Galveston to Vera Cruz. 

 D. variabilis Say. Longer, sculpture feeble. Hatteras to Galves- 

 ton ; W. L? 



