OF CONCHOLOGY. 



155 



tooth-like crenulations. Interior with a purple black nacre. 

 Ventral margin, when normally formed, straight, hut usually 

 arcuated by distortion. Lon. -4, alt. -26, diam. -2 in. Valves 

 from the umbones to the posterior ventral end usually obscurely 

 roundly carinated. 



Habitat, Bay of Yeddo, Japan. Abundant. 



This species, after examination and comparison, was pro- 

 nounced new by the late H. Cuming. It has much the same 

 general aspect as Mytilus glomeratus, Gld. Its solid growth, 

 and the uniform size of a very large series, forbid the idea that 

 it is immature. 



pectinim:. 



PECTEN, Brug. 

 Pecten (Pseudamussium ?) Alaskensis, n. s. 



Shell nearly equilateral, inequivalve, flesh-color with a blush 

 of salmon-color on the umbo of the superior valve. Internally 

 white, the salmon-color showing through the valve. Shell sub- 

 orbicular, barring the auricles, which are wide and prominent. 

 Lower valve flattened, *1 in. smaller than the upper one; sculp- 

 ture 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, prominent, with a deep sinus. Posterior 

 auricle small ; both with strong elevated lines of growth, which 

 rise into scales on the eight or nine fine ribs with which the ante- 

 rior auricle is furnished. Hinge line straight, smooth. Inside 

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

 ating ribs, with traces cf others intercalated near the margin : 

 nodulous or swollen at the more prominent ridges of growth and 

 at the margin. 



Upper 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- 



