364 bulletin: museum of comparative zoology. 



A. Chondrophore supported by two strong props with a cavity between 



them &. S. borealis Totten. 



b. 5. velum Say. 



B. Chondrophore with an anterior prop, extended as a small rib in front of 



the adductor scar, no posterior prop . . &. S. panamensis Dall. 



b. S. occidentalis Deshayes. 



c. S. pusilla Gould. 



C. Chondrophore without props S. volvulus Carpenter. 



III. Ligament opisthodetic, wholly external. 

 3. Subgenus Achaeax Dall. Ligament visible internally only where it crosses the 

 gap between the margins of the valves. Nymphs without props. 



a. S. macrodactifla Rochbrune et Mabille. 



(?) = 5. patagonica Smith. 



b. S.johnsoni Dall. 

 C. <S. agassizii Dall. 



d. S. ventricosa Conr. 



e. »S. grandis Verrill and Bush. 



S. japonica Dunker is the adult of tlie shell named S- pusilla Gould. S. medi- 

 terranea Lamarck is a synonym oi S. solen, as is S. iogata "Poll." 



The geographical distribution of the forms above referred to is as follows : 



5. australis Lamarck, South Australia and New Zealand. 

 5. parkinsonii Gray, New Zealand. 



S. solen von Salis, Mediterranean and Adriatic ; southeastern coast of Spain ; 

 Madeira, and Senegal. 



S. borealis Totten, Halifax, Nova Scotia, to Pensacola, Florida. 



5. velum Say, Halifax, Nova Scotia, to North Carolina. 



5. occidentalis Deshayes, Spezzia, Tripoli, Morocco, Florida Keys, Old 



Providence Island, West Indies, and tlie Yucatan Passage, 2-200 



fathoms. 

 5. panamensis Dall, Santa Barbara, California, south to Panama Bay, 



30-60 fathoms. 

 5. pusilla Gould, Hakodate, Japan, 5 fathoms. 

 S. volvulus Carpenter, San Pedro, California, and south to the Gulf of 



California. 



S. protexta Conrad, from the Miocene of Astoria, if not the young of S. ventri- 

 cosa Conrad, may belong to this subgenus. Modiola linea Iledley, from the 

 Tasman Sea, is suspiciously like a young Acharax. 



fS. agassizii Dnll, from Tillamook Bay, Oregon, to Aguja Point, Peru, 

 1036-1800 fathoms. 

 S. macrndnrti/la R. & M., Orange Harbor, Patagonia, northward to Chilo« 



Island, Southwest Chile, 20-369 fathoms. 

 S- jnhnsnni Dall, Paget Sound to Panama Bay, GO-1740 fathoms. 

 5. ventricosa Conrad, fossil, Miocene of Astoria, Oregon. 

 S. grandis Verrill and Bush, off the eastern coast of the United States, 

 between Chesapeake Bay and Nantucket, in 300 to 1600 fiitiioiiis. 

 V5. patagonica E. A. Smith, west coast of Patagonia. 



I. . 



II. J 



m. 



