DIAGNOSES OF NEW SPECIES OF MARINE BIVALVE MOL- 

 LUSKS FROM THE NORTHWEST COAST OF AMERICA IN 

 THE COLLECTION OF THE UNITED STATES NATIONAL 

 MUSEUM. 



By William Healey Dall, 



Honorary Curator of Mollusks, United States National Museum. 



Having in preparation a check list of the bivalve moUusks con- 

 tained in the marme fauna of the region including the coasts from 

 Point Barrow in the Arctic to San Diego, California, it was found 

 that a comparatively large number of the species in the collection 

 of the United States National Museum were midescribed. 



To avoid launchmg into the literature a quantity of manuscript 

 names the present diagnoses have been prepared. It is hoped at no 

 very distant date to furnish fuller data concerning these species, in- 

 cluding suitable figures. 



In the descriptive matter following, when a station number is given 

 it refers always to the number of a dredging station of the United 

 States Fisheries Steamer Albatross. The data relating to these sta- 

 tions have been printed by the Bureau in its Bulletins. Those species 

 not referred to a station number were collected by private persons, 

 mcluding the writer, at various times during the last sixty-five years, 

 one species having been picked up by Major Rich during the Mexican 

 War. 



The typical specimens are aU preserved in the collection of the 

 United States National Museum. Had the undescribed species be- 

 longmg to the more southern fauna now in the collection been in- 

 cluded, the number would certainly have been greatly increased. 

 These forms, however, are reserved for treatment later. 



In the descriptions when the beaks are said to be a certain distance 

 behind the end of the shell, the distance is measured from a vertical 

 line dropped from the umbo to the basal margin, and at the level of 

 the most distant point of the end of the shell referred to. This vertical 

 line indicates the height, the length being measured on a horizontal 

 line parallel with the base of the shell in a general sense. The diame- 

 ter is the maximum distance from the outside of one valve to the out- 

 side of the other, taken at right angles to the vertical plane of the 

 valves. Measurements are aU in millimeters. 



Proceedings U. S. National Museum, Vol. 52-No. 2183. 



393 



