382 American Seashells 



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. 



