1879.] NATURAL SCIENCES OF PHILADELPHIA. 71 



ON THE NUDIBRANCHIATE GASTEROPOD MOLLUSCA OF THE NORTH 

 PACIFIC OCEAN, WITH SPECIAL REFERENCE TO THOSE OF ALASKA. 



BY DR. R. BERGH, COPENHAGEN. 



PART I. 



The fauna of the North Pacific in general has been but little 

 explored. The number of the so-called Nudibranchiate Gaste- 

 ropod Mollusca found in this region up to this time is rather 

 small. But a few species have been mentioned or described, chiefly 

 by Tilesius, Eschscholtz, and Gould, and the number of forms is 

 much smaller than that which is known from the North Atlantic 

 in the same latitudes. There does not, however, seem to be any 

 reason for a smaller number in the Pacific than in the Atlantic. 



Mr. Dall has been engaged since 1865 in prosecuting researches 

 in regard to the marine invertebrates of the region lying between 

 America and Asia, from latitude 50 to latitude 70 N., including 

 the coasts of Alaska, formerly Russian America, the Aleutian 

 Islands, Bering Sea and Strait, and a part of the Arctic Ocean 

 north of the strait. 



Mr. Dall kindly invited me, who during a series of years have 

 been engaged with studies upon Nudibranchiates, to examine and 

 describe the collections relating to this group ; these were received 

 in the summer of 1876. It has been necessary to include, for 

 comparison, the results of the examination of some few Atlantic 

 species. Dall did not give particular attention to the Nudi- 

 branchs ; yet, while a comparatively small number of forms and 

 specimens have been obtained during his cruises, the number 

 is sufficient to give some idea of the character of this particular 

 fauna and to enrich our knowledge of the groups with several 

 new forms. This will be obvious from the following list: 



o 



NUDIBRANCHIATA OF THE NORTH PACIFIC. 



1. Aeolidia papillosa (L.). 4. Flabellina iodinea (Cooper). 



2. Aeolidia (tw&v.) pacijica, Bergli, 5. Rermissenda opalescens 



n. sp. ? (Cooper). 



3. Goryphella, sp. 



