308 MOLLUSKS OF BERING SEA. 



castanea. It has about five whorls, spirally sculptured; the nucleus 

 smooth and white, the rest waxen, with a pinkish or brownish flush; 

 the surface when denuded of the thin epidermis appears vitreous. The 

 sculpture is not of flattened threads, as in castanea^ but of up to as many 

 as twelve sharp rid<jes, separated by shallow channels or grooves, ex- 

 cavated as if made with a carpenter's oonge; there are sometimes as 

 few as six or seven ridges on th(* body whorl, the others becoming ob- 

 solete. The peritreme is continuous, slightly thickened, with a chiidv in 

 the umbilical region; the total length of the specimen figured is 2.7™'". 

 There is no transverse sculpture, except the faint markings due to 

 lines of growth. The spiral sculpture grows stronger toward the shoul- 

 der of the whorl, as is generally the case, and this tends to give the 

 shell a slightly turreted aspect. 



Alvania auiivillii Dall. ( PL IV, fig.' 8. ) 



Shell waxen or yellowish, with live and a half or six whorls; nucleus, 

 two whorls, white smooth and polished; remainder strongly sculptured 

 with (on the last whorl) about eight strong revolving ridges, narrow 

 but flat toj)[»ed, except in the very young shell, where they are some- 

 times almost sharp-edged ; the anterior and posterior threads are gen- 

 erally the faintest, the others, except in the completely adult, angulate 

 the outer lip at their intersection with it; the one just in front of the 

 suture is sometimes a little nodulous in the early whorls. In the adult 

 the peritreme is simple, continuous, and slightly thickened; there is a 

 distinct though very small umbilicus; the total length of the specimen 

 figured is 4.3'"'". 



I have dedicated this si)ecies, the finest of the group in Alaska, to 

 Mr. Carl Aurivillius, whose work on the gastropods of the Vega expe- 

 dition has recently appeared. Its distinctness from other described 

 northern species has been admitted by all those who have examined it. 

 It seems to have no analogue in European or East American waters. 



The A. auriviUii inhabits the Western Aleutians, where it seems rare. 

 A few specimens were obtained at Adakh Island and one at Constan- 

 tiue Harbor, Amchitka Island, 1874. They were dredged in shoal water 

 near low-water mark. 



Macoma edentula Brod. aud Sby. var. middendorffii Dall. (PI. IV, fig. 11.) 

 M. var. middendorffii Dall, 1. c, p. 347, 1884. 



Since calling attention to the j)robable varietal distinctness of this 

 singular form, I have made a more thorough examination of all the avail- 

 able material, leaving no doubt in my mind of its distinctness from the 

 common T. calcarea Chemn. or lata Midd., a short broad form of which 

 was described by Broderip and Sowerby as T. edentula and well figured 

 in the zoology of the voyage of the Blossom (plate 41, fig. 5, and plate 

 44, fig. 7). T. calcarea is found all over the Alaskan region, and its 

 variety edentula differs from the middendorffii in being of a dull calca- 

 reous or earthy gray or brown with a dark, fugacious epidermis, instead 



