Page:American Seashells (1954).djvu/510

412 Genus Irus Oken 1815 Irus lamellifera Conrad Californlan Irus Venus Plate 3ir Monterey to San Diego, California. 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 Plate 3ih; figure iSd San Mateo County, California, to Lower California. 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 un- necessary 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 Figure 83a, b North Carolina to southeast Florida and the Bahamas.