302 PROCEEDINGS OF THE CALIFORNIA 



Descriptions of New Species of Mollusca from the Northwest 



Coast of America.* 



BY W. H. DALL, U. S. COAST SURVEr. 



Magasella Aleutica, Dall, n. s. (PI. I, fig. 6). 



Shell small, nearly smooth, salmon colored, brighter on the lines of growth, 

 and pale on the umbones ; form subquadrate, anterior edge of haemal valve 

 very slightly excavated, and that of the neural valve correspondingly produced. 

 Loop excessively slender, except the lateral arms of the reflexed portion, which 

 are very broad, but connected behind by a very slender thread of shelly matter, 

 the reflexed portion forming a sort of funnel, opening above, and almost incom- 

 plete behind. Septum thin, rather broad from beliind forward, not produced 

 above the reflexed portion of the loop. Cardinal process and hinge teeth small 

 and inconspicuous, foramen incomplete and horse-shoe shaped, with no vestige 

 of a deltidium. Lat. -35 in., alt. -2 in., Ion. of neural valve -37 in., of haemal 

 valve -33 in. 



Habitat, in the Aleutian Ids, from Akutan Pass, to the Shumagins, attached 

 to the under surface of rocks at extremest low water of spring tides ; Dall. 



This pretty species resembles in miniature Laqueus rubella of Sowerby, but 

 is proportionately shorter and broader. The animal is rather sluggish, and liv- 

 ing specimens kept in sea water for several days exhibited no further signs of 

 life, than the slight opening of the valves. The soft parts are of a darker red- 

 dish color, and show through the shell to some extent, as in Waldheimia venosa. 

 There is some variation in form, some specimens being much broader than 

 others. It was not uncommon, and a number of living specimens were obtained 

 but the details of the anatomy are reserved for another paper to be prepared at 

 a time when I may be able to devote more leisure to the subject. 



ActncEO (Col/iselhi) peramabilis, Dall, n. s. 



Shell thin, delicate, ovate; externally of a uniform dark rose color, with a 

 few scattered irregular blotches of light or dark brown, nucleus pale. "Within 

 polished, bluish white, with a chestnut brown spectrum with sharply defined 

 edges, outside of which for a short distance the white is unsullied, but further 

 toward the margin in adult specimens, radiating brown blotches may be ob- 

 served forming a more or less interrupted band around the shell, which is 

 wanting in the young. The margin is of the same deep rose as the exterior. 

 Shell moderately elevated, with the apex well marked subacute and situated in 

 the central third. Nucleus smooth, pale, sharply decurved with a chink 

 beneath it, in front. Sculpture of fine sharp elevated threads which extend 

 from the vertex to the margin without bifurcating. These are crossed by very 

 fine sharp lines of growth slightly elevated. Lon. 1-03 in., lat. 0-8 in., alt. 

 0'33 in. Posterior slope slightly arched. 



Habitat, Shumagin group of islands, Alaska Territory, on rocks near low 

 water mark. Dall. 



* Printed in advance, December 17, 1872. 



