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382 sinus will distinguish this clam from the true Quahogs (see Mercenaria mercenaria). A common, commercially dredged species found in sandy mud from 5 to 80 fathoms. This is the only living species in this family. There are numerous fossil species. Also called the Black Clam and Mahogany Clam. Family TRAPEZIIDAE Genus Coralliophaga Blainville 1824 Shell cigar-shaped, with the beaks at the anterior end. 3 cardinals in each valve, the posterior one extending along the hinge line like a lateral. Posterior muscle scar considerably larger than the anterior one. Some work- ers have placed this genus in the Petricolidae. Coralliophaga coralliophaga Gmelin Coral-boring Clam Plate 28p West coast of Florida to Texas and the West Indies. % to I % inches in length, oblong to elongate, and quite thin. Very finely sculptured with radial threads. Concentric lamellations present at the posterior end. Exterior yellowish white; interior white. This shell is very similar in appearance to Lithophaga antillarum, but may be told from it by the presence of distinct teeth in the hinge. This is an uncommon species which lives in the burrows of other rock-boring mollusks. Superfainily DREISSENACEA Fajnily DREISSENIDAE Genus Cojigeria Partsch 1835 Subgenus Mytilopsis Conrad 1857 Congeria leucophaeata Conrad Conrad's False Mussel New York to Florida to Texas and Mexico. V2 to % inch in length, superficially resembling a Mytiliis or Septifer because of its mussel-like shape. The Septifer-like shelf at the beak end has a tmy, downwardly projecting, triangular tooth on the side facing the long, internal ligament. The hinge has a long thin bar under the ligament. Exte- rior bluish brown to tan with a thin, somewhat glossy periostracum. Interior dirty bluish tan. This common bivalve attaches itself by its short byssus to rocks and twigs in clumps which resemble colonies of Mytihis. Found in brackish to fresh water near rivers.