Page:American Seashells (1954).djvu/436

354 Genus Septifer Recluz 1848 Septifer bifurcatus Reeve Bifurcate Mussel Crescent City, California, to Gulf of California. I to 2 inches in size, subtriangular in outline, inflated. With a couple of dozen strong, wavy radial ribs. Inner margin crenulated. Periostracum black, although often worn white between the ribs. Interior pearly-white, often stained bluish brown on one half of the inner side. The subspecies obsoletus Dall from San Diego is mostly black on the interior and is a quite elongate form. Genus Mytilus Linne 1758 Mytilus edulis Linne Blue Mussel Plate 35m Arctic Ocean to South Carolina. Alaska to CaHfornia. 1 to 3 inches in length, no ribs but often with coarse growth lines. Ventral margin often curved. Color blue-black with eroded areas of chalky purplish. Periostracum varnish-like. Interior slightly pearly-white with deep purple-blue border. Occasionally, specimens have radial rays of brown- yellow. Very common in New England. Sometimes found in more south- erly waters attached to floating wood. Mytilus edulis diegensis Coe 1946 (Northern California to Lower Cali- fornia) is indistinguishable from specimens of edulis found in Alaska and New England, and probably only represents an ecological or physiological race (see W. R. Coe, 1946). Mytilus calif ornianus Conrad Calif ornian Mussel Plate 19P Aleutian Islands to Socorro Island, Mexico. 2 to 10 inches in length, thick, inflated; ventral margin nearly straight; with less than a dozen or so, fairly broad, weak radial ribs which are best seen on the middle part of the shell. Growth lines very coarse. An abun- dant species found between tides attached to rocks. Genus Musculus Roding 1798 Mussel-like shells with the sculpturing divided into three oblique areas, the center one being smooth or almost so, and the two end areas having radial ribs. The ligament is much longer than that in Crenella. These are moderately deep-water clams. Mantle folded in front into a wide, incurrent