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346 Subgenus Cunearca Dall 1898 Anadara brasiliana Lamarck Incongruous Ark Plate 27y North Carolina to West Florida to Texas and the West Indies. I to 1V2 inches in length; almost as high as long. Beaks facing each other at center of short, transversely striate ligamental area. Left valve over- laps right valve considerably. Ribs 26 to 28, square with strong bar-like beads. Periostracum thin, light-brown. A. mcongnia Say is this species. A. chemnitzi Philippi from the Greater Antilles to Brazil is similar, but thick-shelled, less than i inch in length; the beaks are slightly forward of the center of the ligamental area. Subfamily NOETllNAE Genus Noetia Gray 1857 Beaks point posteriorly; valves the same size; ligament transversely stri- ate; posterior muscle scar raised to form a weak flange. Subgenus Eontia MacNeil 1938 The subgenus Eontia is an Atlantic group only. Noetia s. str. differs in having decidedly more regular sculpture, the ribs smoother and never di- vided; deeper and longer crenulations on the inner margin. There is only one Recent American true Noetia (reversa H. and A. Adams) which occurs from the Gulf of California to Peru. Noetia ponderosa Say Ponderous Ark Plate 27Z; figure 28a Virginia to Key West, Louisiana and the Gulf of Mexico. 2 to 2 % inches in length, almost as high as long. Ribs raised, square and split down the center by a fine incised line; 27 to 31 ribs per valve. Posterior muscle scar raised to form a weak flange. Periostracum thick, black, but wears off at the beaks. A common shallow-water sand-dweller. Fossil speci- mens are rarely found on Nantucket, Massachusetts, beaches. Family LIMOPSIDAE Genus Limopsis Sasso 1827 Rather small, obliquely oval, clams with tufted, velvety brown peri- ostracum. Hinge line curved, with a series of oblique teeth. The hinge resembles that of the Glycymeridae. Ligament external, small, central, tri-