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412 American Seashells
Genus Irus Oken 1815
Irus lamellifera Conrad Californlan Irus Venus
Monterey to San Diego, California.
Plate 3ir
I to I % inches in length, usually oblong, although some specimens may
be almost round. Characterized by about a dozen, strongly raised, concentric
lamellae or thin ridges. Shell whitish and with a chalky texture. Moderately
common. Found burrowing in gray shale from low water to several fathoms.
Subfamily MERETRICINAE
Genus Tivela Link 1807
Tivela floridana Rehder Florida Tivela
Palm Beach County, Florida.
% inch in length, subquadrate, beaks in the center, highly polished and
with microscopic growth lines near the margins. Exterior glossy, tan or
purplish. Interior mottled with purplish brown. This is the only Tivela
recorded from eastern United States. Uncommon offshore.
Subgenus Pachydesma Conrad 1854
Tivela stultorum Mawe Pismo Clam
San Mateo County, California, to Lower California.
Plate 3ih; figure iSd
3 to 6 inches in length, ovate, heavy, moderately inflated, glossy-smooth,
except for weak lines of growth. Ligament large and strong. Color brownish
cream with wide, mauve, radial bands. Bands may be absent. Posterior end
marked off by a single, sharp thread. Lunule lanceolate and with vertical
scratches. Periostracum thin and varnish-like. A common and edible species.
This is the only West Coast Tivela, but it has received a number of unnecessary
names, T. crassatelloides Stearns being one of many.
Genus Transennella Dall 1883
Left anterior lateral fitting into a socket in the right valve. Internal
margins arc obliquely grooved with numerous, microscopic lines. These
are parallel to the growth lines at the ventral margin of the valves.
Transennella stimpsoni Dall Stimpson's Transennella
North Carolina to southeast Florida and the Bahamas.
Figure 83a, b