No. 3. — Reports on the ResxiUs of Dredging, under the Supervision 

 of Alexander Agassiz, in the Gulf of Mexico, 1877-78, hy the 

 ,United States Coast Survey Steamer " Blake !' Lieutenant-Com- 

 mander C. D. SiGSBEE, U. S. N., Commanding. 



(Publislied by permission of Carlile P. Patterson, Supt. U. S. Coast Survey.) 



V. , 



General Conclusions from a Preliminary Examination of the Mollusca, 



by W. H. Ball. 



The collection made by Mr. Agassiz and Lieut. -Com. Sigsbee on 

 board the " Blake " contained about five hundred species, from which 

 the Pteropods and some other groups have been excluded, as will be 

 seen by the tables, leaving 462 species to be considered in this paper. 



Of course the specific determination of all these forms is a task which 

 must necessarily occupy a large amount of time and labor, and if that 

 had been a necessary preliminary to a report of any kind I should have 

 nothing to say on the subject at the present time. Fortunately, how- 

 ever, the generic affiliations can be approximately determined almost at 

 sight, and species may be almost as readily separated from one another 

 by a practiced eye ; so that it is not necessary to wait for the comple- 

 tion of the drudgery of researches into the nomenclature of the various 

 specific forms before announcing any general conclusions. 



Before proceeding to these it is necessary to make a few preliminary 

 statements. 



L The observations herein tabulated are not to be taken as exact in 

 every instance. The limits of a species, or the reference to a subordi- 

 nate generic group, is liable to be modified, occasionally, by more mature 

 study. The examination of the collections for 1878-79, made under 

 the supervision of Mr. Agassiz on board the "Blake," will doubtless 

 add to, and in some instances change, the figures deduced from the coir 

 lections of the previous season ; all that is claimed for the conclusions 

 here put forward is, that the general character of them seems already to 

 be sufficiently established by the evidence in hand. 



VOL. VI. — NO. 3. 7 



