354 Ainerican Seashelh 



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 



