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342 arks can be placed under the single genus Area. The geological history and morphological studies force us to recognize three subfamilies. Many of the subgenera listed here are considered by some authorities as full genera. 1 have refrained from defining their limits. Subfamily ARCINAE Genus Area Linne 1758 Characterized by the long, narrow hinge line with numerous small teeth, by the large byssal notch on the ventral side, and the wide ligamental area between the beaks. Area zebra Swainson Turkey Wing Plate 2711 North Carolina to Lesser Antilles. Bermuda. 2 to 3 inches in length, about twice as long as deep. Color tan with flecks and zebra-stripe markings of reddish brown. Periostracum brown, matted. Ribs of irregular sizes. No concentric riblets. Do not confuse with A. umbonata. A common species which attaches itself to rocks with its byssus. Used extensively in the shellcraft industry. Formerly A. oceiden- talis Philippi. Area wnbonata Lamarck Mossy Ark Plate 27] North Carolina to the West Indies. i^ to 2% inches in length. Similar to A. zebra, but differing in having beaded ribs and a very large byssal opening, usually having the posterior end much larger, and in lacking the zebra stripes. Periostracum sometimes quite heavy and foliated. Commonly attached to underside of rocks in shallow water. Genus Barbatia Gray 1847 Subgenus Barbatia s. str. Barbatia eandida Helbling White Bearded Ark Plate 271 North Carolina to Brazil. 1/4 to 1V2 inches in length; fairly thin, not heavy. Irregular in shape. Byssal opening at base of shell. Numerous weak, slightly beaded ribs; those on the posterior dorsal area being very strongly beaded. Periostracum brown, longest at posterior end. Exterior and interior of shell white. Liga-