SUMMARY OF THE MARINE SHELLBEARING MOLLUSKS 
OF THE NORTHWEST COAST OF AMERICA, FROM 
SAN DIEGO, CALIFORNIA. TO THE POLAR SEA, MOST- 
LY CONTAINED IN THE COLLECTION OF THE UNITED 
STATHS NATION AF. MUSEUM, WITH ILLUSTRATIONS 
OF HITHERTO UNFIGURED SPECIES. 
By William Healey Ball. 
Honorary Curator of Mollusks, United States National Museum. 
INTRODUCTION. 
To the preparation of this summary the author has brought the 
results of more than 50 years’ study of the molluscan fauna of the 
northwest coast, his personal investigations in the field having begun 
in 1865, when, under the auspices of the Smithsonian Institution, he 
visited the shores of the Pacific as a member of the scientific corps of 
the Western Union Telegraph Expedition. 
Since that time a constant inflow of material from that region has 
enriched the collection of the United States National Museum until 
it has become unrivaled in this group of animals. 
Very few of the species described from the area between the 
southern boundary of the United States and the Polar Sea on the 
Pacific coast are absent from the series referred to. In a few cases 
where the writer has not been able to verify personally the names or 
the distribution from authentic specimens, the name of the authority 
upon whom the data rest has been added in parentheses. 
The distribution of the Mollusca on the west coast of America may 
be allotted to three grand divisions : the Arctic or Boreal, the Tem- 
perate, and the Tropical faunas. 
The first, containing many Circumboreal species, extends from the 
Arctic or Polar Sea to the southern limit of drift ice in winter in 
Bering Sea. 
The Temperate division extends from this line southward on the 
west coast of America to Point Conception, California. 
The Tropic division extends from this point southward to Point 
Aguja on the coast of Peru. 
Each of these divisions may be subdivided into subordinate and 
reasonably distinct faunas; the Arctic into Eastern and Western, or 
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