MUSEUM OF COMPAKATIVE 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 laniellas, 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 lamellae, 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 lirse (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, Ion. 

 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 

 143, off Saba Bank, in 150 fms., bottom temperature 63°. 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. 



Amusiiun (Propeamusiuin) Alaskensis Dall. 



Pecten (Pseudamussium ?) alaskensis Dall, Am. Journ. Conch., 1871, p. 155, 



PI. 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, 



