2 BULLETIN 112, UNITED STATES NATIONAL MUSEUM. 
Atlantic and Pacific; the Temperate into Aleutian, Oregonian, and 
Californian; the Tropic into Gulf of Californian, Panamic, and 
Ecuadorian. These divisions coincide with differences of tempera- 
ture of the sea water, generally indicated by the distribution of 
ocean currents. 
Taking the distribution of a single family these distinctions might 
have their boundaries somewhat modified, but on the average of the 
whole molluscan fauna they appear to be well established. 
The limits of these faunas are not in all cases sharply defined. 
Some of the less sensitive species will be found to range far beyond 
the divisional boundaries. In southeastern Alaska, where the in- 
shore channels of the Alexander Archipelago are kept cold by the 
drainage from glacier streams, many Arctic forms persist; perhaps 
relicts from the glacial period; while on the outer fringe of ' the 
islands quite a number of the more southern species extend their 
range northward in the warmer ocean waters. 
The student of this list will notice many more species, which from 
southern California extend their range to Panama or even Peru, than 
are recorded in any previous publication. 
There is a special faunula existing on the shallow plateau of 
northeastern Bering Sea. It is composed largely of carnivorous 
gastropods, which do not approach the shores. This has furnished 
a multitude of Buccinidae to the present summary, and was, before 
the incursion of the whaling fleet, the summer feeding ground of 
vast numbers of the Pacific walrus. 
Before concluding this introduction it would be improper to omit 
a few words of gratitude to the numerous private students and col- 
lectors whose investigations and contributions to the collection have 
added a multitude of new forms to the known fauna, and to whom a 
large part of such completeness as this summary may possess is 
necessarily due. Detailed acknowdedgments must await another 
occasion, but the evidence of their activities is on permanent record 
in the collections of the United States National Museum, and v/ill 
afford to future students an indispensable basis for study. 
Acknowledgment must also be made to the Director of the United 
States Geological Survey for the opportunity afforded me to work 
upon and publish the present paper. 
In indicating a figure illustrative of the species standard works, 
such as are generally accessible in large libraries, have been chosen 
when possible. If the figure in the work referred to bears there a 
different specific designation from the one here adopted, it may be 
understood that the former name is a synonym of the one used in this 
summary, or for some other reason is not accepted. 
Every effort to keep the classification adopted as up to date as 
possible has been made; though this is a subject on which differences 
