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334 % inch in length, thin, translucent. Periostracum shiny, light-brown, with slender, radial lines of darker brown which are finely striate posteriorly. Ligament bounded by a single, arched prop or rib. Uncommonly dredged offshore. Order PROTOBRANCHIA Suborder NUCULACEA Key to Families a. Chondrophore below hinge present: b. External ligament absent; shell ovate Nuculidae. bb. External ligament present; shell elongate .... Nuculanidae. aa. Chondrophore absent; shell ovate Malletiidae. Family NUCULIDAE Genus Nucula Lamarck 1799 Shell ovate, usually less than Yz inch in size; interior pearly; ventral mar- gins usually with fine denticulations.

Figure 70. Atlantic Coast Nut Clams, a and b, Nucida proxima Say, ^ inch; c, N. tenuis Montagu, Yo inch (both coasts); d, N. delphinodonta Mighels, Yiq inch; e, N. atacellaim Schenck, Y& inch. Subgenus Nucula s. str. Nucula proxima Say Nova Scotia to Florida and Texas. Atlantic Nut Clam Figure 70a, b % inch in length, obhquely ovate, smooth. Color greenish gray with microscopic, embedded, axial, gray lines and prominent, irregular, brownish, concentric rings. Outer shell overcast with oily iridescence. Anterior end often with microscopic, axial lines. Ventral edge minutely crenulate. Com- mon just offshore in mud.