364 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
A, Chondrophore supported by two strong props with a cavity between 
TO oca. o E os Nos oral Totem 
b. S. velum Say. 
B. Chondrophore with an anterior prop, extended as a small rib in front of 
the adductor scar, no posterior prop . . a. S. panamensis Dall. 
b. S. occidentalis Deshayes. 
c. S. pusilla Gould. 
C. Chondrophore without propa . . . . . . .  S.valvulus Carpenter. 
III. Ligament opisthodetic, wholly external. 
8. Subgenus Acmarax Dall. Ligament visible internally only where it crosses the 
gap between the margins of the valves. Nymphs without props. 
a. 5. macrodactyla Rochbrune et Mabille. 
(2) = S. 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 the shell named S. pusilla Gould. S. medi- 
terranea Lamarck is a synonym of $. solen, as is 8. togata “Poli.” 
The geographical distribution of the forms above referred to is as follows : 
S. australis Lamarck, South Australia and New Zealand. 
I. J S. 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. 
S. velum Say, Halifax, Nova Scotia, to North Carolina. 
S. occidentalis Deshayes, Spezzia, Tripoli, Morocco, Florida Keys, Old 
Providence Island, West Indies, and the Yucatan Passage, 2-200 
IL J fathoms. 
S. panamensis Dall, Santa Barbara, California, south to Panama Bay, 
30-60 fathoms. 
$5. pusilla Gould, Hakodate, Japan, 5 fathoms. 
S. valvulus 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 Hedley, from the 
Tasman Sea, is suspiciously like a young Acharax. 
(5. agassizii Dall, from Tillamook Bay, Oregon, to Aguja Point, Peru, 
1036-1800 fathoms. 
S. macrodactyla R. & M., Orange Harbor, Patagonia, northward to Chiloé 
Island, Southwest Chile, 20-869 fathoms. 
S. johnsoni Dall, Puget Sound to Panama Bay, 60-1740 fathoms, 
S. 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 800 to 1600 fathoms. 
S. patagonica E. A. Smith, west coast of Patagonia. 
II. 
