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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
West coast of Florida to Texas and the West Indies.
% to I %
Plate 28p
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.