No. 6. — Reports on the Dredging Operations off the West Coast of 

 Central America to the Galapagos, to the West Coast of Mex- 

 ico, and in the Grulf of California, in charge of Alexander 

 Agassiz, carried on hy the U. S. Fish Commission Steamer 

 " Albatross " during 1891, Lieut. Commander Z. L. Tanner, 

 U. S. N., Commanding, XXXVIII. 



AND 



Reports on the Scientific Results of the Expedition to the Eastern 

 Tropical Pacific in charge of Alexander Agassiz, bg the 

 U. S. Fish Commission Steamer '' Albatross,'' from October, 

 1904, to March, 1905, Lieut. Commander L. M. Garrett, 

 U. S. N., Commanding, ^lY . 



Reports on the Mollusca and Brachiopoda. 

 By William Healey Dall. 



Introduction. 



The following report includes in the material treated of, first, the 

 Mollusca and Brachiopoda collected by the U. S. S. "Albatross" during 

 the cruise of February to April, 1891, under the direction of Dr. 

 Agassiz ; and, secondly, further material obtained during the voyage of 

 1904-.5, under the same auspices. 



At tiie suggestion of Dr. Agassiz, the moUuscan material of the last 

 voyage having proved small in amount though most interesting in 

 quality, the report was extended to cover both voyages, and for com- 

 pleteness' sake I have added a few species obtained in the same region by 

 the " Albatross " during 1888, while on her way from the Atlantic to Cali- 

 fornia, and which had remained without being worked up, having come 

 into my custody after my report on the voyage of 1887-8 had boon 

 printed. The few deep-water forms, as well as the shoi"e and roof shells 

 obtained during the Expedition to the Tropical Pacific, August, 1899, to 

 March, 1900, are also included. 



