MUSEUM OF COMPARATIVE ZOOLOGY. 215 
twelve radiating ridges between which toward the base intercalary ridges rap- 
idly appear, so that at the base, in one specimen, there are thirty-two ridges 
and beginnings of ridges; over the whole are set closely declining concentri- 
cally continuous lamell, uniform, when unbroken, over ridges and intervals ; 
the ears are nearly equal, similarly sculptured to the rest, and with three to 
five radiating ridges ; the cardinal line straight and the umbo not prominent ; 
the left valve is a little smaller, smooth or not ridged, and covered with simi- 
lar but less elevated and closer lamelle, which swell up in obsolete radiating 
lines in sympathy with the ridges of the other valve, but which swellings do 
not cover any genuine ridges ; ears subequal, similarly sculptured; byssal notch 
not deep ; interior of valves with 10 to 16 radiating lire (beside the crura) of 
which about 10 run home to the body of the valve ; ligamental pit moderate, 
hinge line simple and without transversely rugose areas ; max. alt. 15.5, lon. 
15.0, hinge line 7.0, diam. 3.0 mm. 
Soft parts yellowish white except the liver; “ocular” tubercles without 
pigment, but present. 
Dredged off Morro Light, Havana, at Stations 16 and 100, in 250-400 fms., 
living, bottom temperature 55°.6 F. A single valve was obtained .at Station 
148, off Saba Bank, in 150 fms., bottom temperature 638°.5 F. 
This pretty species is nearest to A. squamigerum E. A. Smith, having the 
same type of concentric sculpture on the right valve, but differs in the strong 
rectilinear character of the radiating ribs, in being proportionally wider and 
more inequilateral, having a wider and less oblique hinge line, and being 
apparently somewhat flatter. These differences, however, though strong as 
regards the figured specimens, might be less evident for a large series. Still, 
they are so marked for what we have, that I have thought it perhaps better to 
give the present form a separate name than to assume the existence of inter- 
mediate varieties, without any intermediate material. 
Amusium (Propeamusium) Alaskensis Datt. 
Pecten (Pseudamussium ?) alaskensis Dati, Am. Journ. Conch., 1871, p. 155, 
Pl. xvi. fig. 4 a, b. 
Plate V. Figs. 7, 7 a 
In order to bring together the available material relating to this group, this, 
the largest species yet known, and having the most numerous ribs, has been 
included in the figures. So far it has occurred only on the Alaskan coast, and 
no other species is known from there; but there are several in the waters of 
Japan and Korea. 
