ITo. 6. — Reports on the Results of Dredging, under tJie Supervision 

 of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in 

 the Caribbean Sea (1879-80), hy the U. S. Coast Survey Steamer 

 "Blake" Lieut.-Commander C. D. Sigsbee, U. S. K, and Com- 

 mander J. E. JBartlett, U. S. N., Commanding. 



(Published by permission of (Jarlile P. Patterson and J. E. Hilgapd, Superin- 

 tendents of tlie U. S. Coast and Geodetic Survey.) 



XXIX. 



Report on the MoUitsca, hy W. H. Dall. — Part I. Brachiopoda and 



Pelecypoda. 



In 1878, the moilusks of the " Blake " were intrusted to me for exami- 

 nation and report, and a Preliminary Note upon them appeared in August 

 of that year (Bull, Mus. Comp. Zool., Vol. V. No. 6, pp. 60-62). 



The following season a second instalment was received, and, in Feb- 

 ruary, 1880, after a cursory examination of the material, I was enabled 

 to furnish Prof, Agassiz with a short resume of the general conclusions 

 which seemed to result from the data obtained by that examination 

 (Bull. M, C. Z., Vol. VI, No. 3, pp. 85-93). 



My time during ordinary working hours being absorbed by official 

 duties, and the entire period from February, 1880, to January, 1881, 

 being occupied by field-work on the Pacific coast, progress has neces- 

 sarily been slow ; the more so, as nearly all the material consists of 

 specimens so small as to require reiterated scrutiny under a glass to 

 determine their characters. To separate and label the specimens con- 

 tained in nearly two hundred different lots, to select specimens for 

 figuring and to scrutinize and revise the drawings, to search the lit- 

 erature relating to moilusks for the scattered data in relation to such 

 as are native to the region in question, and to accurately describe such 

 species as seemed to be new, has been the task before me, to be carried 

 out in the scanty leisure afforded by such evenings and holidays as were 

 not necessarily otherwise employed. The delay in completing the work, 

 it will be seen, has been inevitable under the circumstances, and my 

 thanks are due to Prof, Agassiz, and others interested, for the patience 

 with which they have kept these circumstances in mind. 



VOL. XII. — NO. 6, 11 



