DIPLODONTIDAE 383 



Super jamily LUC IN ACE A 



Family DIPLODONTIDAE 



Genus Diplodonta Bronn 1831 



Shell thin, orbicular and strongly inflated. There are 2 cardinal teeth in 

 each valve. The left anterior and right posterior ones are split or bifid. Lat- 

 erals obscure or absent. Taras Risso, commonly used in place of the name 

 Diplodonta, is a doubtful name which has been recently abandoned. 



Subgenus Diplodonta s. str. 

 Diplodonta punctata Say Common Atlantic Diplodon 



North Carolina to both sides of Florida and the West Indies. 



% to % inch in length, moderately strong, almost orbicular, well-inflated 

 and pure-white in color. Smooth near the beaks, elsewhere very finely 

 scratched with concentric lines and commonly with distantly spaced, coarse 

 growth lines. Fairly common in shallow to deep water. 



Diplodonta orbella Gould Pacific Orb Diplodon 



Alaska to Panama. 



% to I inch in length, almost circular in outline, quite inflated and 

 smoothish except for moderately coarse growth lines. Beaks small, pointing 

 slightly forward. Ligament posterior to beaks is long, raised and conspicuous. 

 2 rather large teeth in each valve below the beaks. Left anterior and right 

 posterior teeth split. In many shallow-water localities, this clam builds a 

 compact nest of periostracal material and detritus. In its more southerly 

 range, specimens are usually more compressed, less orbicular in shape and 

 more glossy externally (subspecies subquadrata Carpenter). Alias Taras or- 

 bella. 



Subgenus Phlyctiderma Dall 1899 

 Diplodonta semiaspera Philippi Pimpled Diplodon 



North Carohna to Florida, Texas and the West Indies. 



Rarely over V2 inch in length, similar to D. punctata, but chalky-white 

 externally and with numerous concentric rows of microscopic pimples. Mod- 

 erately common in sand below low-water mark to 40 fathoms. Alias D. 

 granulosa C. B. Adams. 



