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Rh 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.