COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 19 



Pseudamusiuni simanense Kuroda, 1931, pp. 72, 73, figs. 92, 93. Plio- 

 cene, Pleistocene and Recent of Japan. 

 Pseudarnussium (Cyclopecten) simanense Kuroda, 1931, p. 81. 

 Pecten (Propeamussium) alaskensis Dall. Grant & Gale, 1931, p. 234. 

 "Living: Alaska to Magdalena Bay, Lower California, usually in 

 deep water; Japan." Also previous Pliocene and Pleistocene records. 

 Polynemamussium alaskense (Dall). Habe, 1951, p. 72. 

 Propeamussium alaskense (Dall). Kuroda & Habe, 1952, p. 29. Pacific: 

 39° N— 56° N; Japan Sea: 36° N— 43° N. 

 Holotype'. U. S. National Museum. 

 Type locality : Port Etches, Chugach Gulf, Alaska. 

 Original description : Shell nearly equilateral, inequivalve, flesh-color 

 with a blush of salmon-color on the umbo of the superior valve. Intern- 

 ally white, the salmon-color showing through the valve. Shell suborbi- 

 cular, barring the auricles, which are wide and prominent. Lower 

 [right] valve flattened, .1 in. [2.5 mm] smaller than the upper one; 

 sculpture of fine, close, equal, concentric ridges, sharply defined and 

 separated by narrow non-canaliculated grooves. Valve covered with a 

 fine velvety epidermis, ashy and very finely radiately striate. Surface of 

 the valve, except for the ridges, smooth. Anterior auricle long, prom- 

 inent, with a deep sinus. Posterior auricle small; both with strong ele- 

 vated lines of growth, which rise into scales on the eight or nine fine ribs 

 with which the anterior auricle is furnished. Hinge line straight, smooth. 

 Inside of the valve polished, furnished with twenty-one rounded, radi- 

 ating ribs, with traces of others intercalated near the margin ; nodulous 

 or swollen at the more prominent ridges of growth and at the margin. 

 Upper [left] valve similar, inside; anterior auricle shorter, not so 

 deeply sinuated. Valve more convex than the under one, and a little 

 larger. Dorsal areas finely granulate. Umbo smooth ; half way toward 

 the margin the striae of increase become more conspicuous, and about 

 thirty-five pseudo-ribs radiate toward the margin. These are formed by 

 the elevation of the concentric lines of growth like ruffles, in such a way 

 that the edge of one fluting of the ruffle overhangs the beginning of the 

 next, and so on. These are very fragile, and when broken away show the 

 nearly smooth surface of the valve underneath, without any true rib at 

 all. Faint grooves are intercalated between the pseudo-ribs toward the 

 margin. Lon. .76, alt. .76, diam. .22 in., width of hinge line .34 in. 

 Angle at the umbones, 100°. [Height, 19.5 mm; breadth, 19.5 mm; 

 hinge line, 9 mm ; diameter, 5 mm; umbonal angle, 100°.] 



Additional descriptive notes: Among eastern Pacific specimens the 

 criteria given by Dall are quite constant. Japanese specimens have the 



