Preliminary Deseriptions of New Speeies of Mollusea froin 
thè Northwest Coast of America. 
BY W. H. DALL, D. S. COAST S0EVEY. . 
[From thè Proceedings of Vie California Academy of Sciences^ pHnted in advance, Dee. 17, 1872.] 
Magasella Aleutica, Dal!, n. s. 
Shell small, nearly smootb, salmon colored, brighter on thè lines of growtli, 
and pale on thè umbones ; form subquadrate, anterior edge of htemal valve 
very slightly excavated, and that of thè neural valve correspondingly produced. 
Loop excessively slender, except thè luterai arms of thè reflexed portion, which 
are very broad, but connected behind by a very slender thread of shelly matter, 
thè reflexed portion forming a sort of funnel, opening above, and almost incom- 
plete behind. Septura thin, rather broad from behind forward, not produced 
above thè reflexed portion of thè loop. Cardinal process and hinge teeth small 
and inconspicuous, foramen incomplete and horse-shoe shaped, with no vestige 
of a deltidium. Lat. -3.5 in., alt. -2 in., lon. of neural valve -37 in., of haemal 
valve ‘33 in. 
Habitat, in thè Aleutian Ids, from Akutan Pass, to thè Shumagins, attached 
to thè under surface of rocks at extremest low water of spring tides ; Dall. 
This pretty speeies resembles in miniature Laqueus ruhella of Sowerby, but 
is proportionately shorter and broader. The animai is rather sluggish, and liv- 
ing specimens kept in sea water for several days exhibited no further signs of 
life, than thè slight opening of thè valves. The soft parts are of a darker red- 
dish color, and show through thè shell to some extent, as in Waldiieimia venosa. 
There is some variation in form, some specimens being much broader than 
others. It was not nncommon, and a number of living specimens were obtained, 
but thè details of thè anatomy are reserved for another paper to be prepared at 
a time when I may be able to devote more leisure to thè subject. 
Acmeea [Collisella) peramabilis, Dall, n. s. 
Shell thin, delicate, ovate; externally of a uniforra dark rose color, with a 
few scattered irregular blotches of light or dark brown, nucleus pale. Within 
polished, bluish white, with a chestnut brown spectrura with sharply defined 
edges, outside of which for a short distance thè white is nnsullìed, but further 
toward thè margin in adult specimens, radiating brown blotches may be ob- 
served forming a more or less interrupted band around thè shell, which is 
wanting in thè young. The margin is of thè same deep rose as thè exterior. 
Shell moderately elevated, with thè apex well marked subacute and situated in 
thè centrai third. Nucleus smooth, pale, sharply decurved with a chink 
