Preliminary Descriptions of New Speeies of Mollusca from thè 
Coast of Alaska with notes on some rare forms. 
3Y W. H. DALL, U. S. COAST SURVEV 
iFrom tke Praceedings oftke California Academy of Scititces, pìnnled iti advance. Aprii 9, 1873.] 
While thè fioal deseription and thorough examinatioa of thè coUections of 
marine invertebrates, niade by me on thè coast of our new Territory, are neces- 
sarily delayed, it seems desirable to put on record a few of thè more striking 
facts, and to describe some of thè more remarkable forms which bave thus come 
under ray notice. I bave already given to thè Academy preliminary descriptions 
of a few of thè speeies which appear to bave been hitherto unknown, and this 
paper contains additional material of thè same kind, though my time has been 
so much engaged by other and more pressing duties, tbat a very large amount 
of work of this kind stili remains unfinished. 
In thè matter of distribution it has been pretty well deraonstrated by our re- 
searches that three faunae come together and are more or less intermingied in thè 
region between Unalashka and thè Shumagins. The Shumagin group of islands, 
jutting out from thè main land and deflecting thè coast current more or less to 
thè southward off shore, acts toward thè Oregonian fauna (which I extend from 
Monterey to thè Shumagins), as Cape Cod on thè east coast of North America 
does to thè fauna which charaeterizes thè coasts of thè Middle and Southern 
States. 
In this group many of thè charaeteristic animals of thè Oregonian fauna, 
such as Mytilus californicus, Piirpura lactuca, Amphissa corrugata, Mccra var- 
iegata and Petricola carditoides, attain their most western limit. The Arctic 
fauna which charaeterizes thè shallow waters of Bering Sea and thè Arctic 
Ocean, is well represented by forms of Astarte, Buccinum glaciale, cyaneum and 
ciliatum. Scalarla grònlandlcum, Cardium islandicum. Lacuna vincta, several 
speeies of Bela, Admete and Odostomia, and many others which pass, in most 
cases, but little to thè eastward. The typieal Aleutian fauna, which was (up 
to thè commencement of our researches in 1865) almost unknown, is character- 
ized here by such speeies as Pecten alaskensis, Drillia Kennicottii, Rictocyma 
mirahilis. Voluta Stearnsii, Magasella aleutica, Litorina aleutica, Acmma syba- 
ritica, peramabilis and Macella rosea, Heliotropis liarpa, and other forms described 
in this paper. Much remains to be done in traeing thè course and eharacteris- 
tics of this fauna to thè westward, which I hope during thè coraing season to 
elucidate to some extent, The following speeies possess peculiar interest as be- 
