552 report — 1884. 



and especially that of the late Professor Stimpson at Chicago. The kind- 

 ness of Professor Spencer Baird enabled me to witness the dredgings 

 which were then carried on along the coast of New England under the 

 charge of the eminent and still living zoologist; Professor Verrill, of Yale 

 College. 



The result of these examinations was communicated by me to the 

 British Association at their Brighton Meeting in the following year, under 

 the title of ' The Mollusca of Europe compared with those of Eastern 

 North America.' I estimated the former to consist of about 1,000 species 

 (viz., 200 land and freshwater, and 800 marine), and the latter to consist 

 of about 400 species (viz., 110 land and freshwater, and 290 marine) ; 

 and I took Mr. Binney's edition of Professor Gould's ' Report on the 

 Invertebrata of Massachusetts,' published in 1870, as the standard of 

 comparison for the American Mollusca. That work gave 401 species, of 

 which I considered 41 to be varieties and the young of other species, 

 leaving 360 apparently distinct species. I reckoned that about 40 species 

 might be added in consequence of the later researches of Professor Verrill 

 and Mr. Whiteaves on the coast of New England and in the Gulf of St. 

 Lawrence. I may here observe, by way of parenthesis, that the relative 

 number of species above mentioned has since been considerably increased, 

 both on the European and American continents, although the proportions 

 may not be very different. I proceeded to identify 173 out of the 360 

 Massachusetts species as European — viz., land and freshwater 39 (out 

 of 110), and marine 134 (out of 250), the proportion in the former case 

 being 28 per cent., and in the latter nearly 54 per cent. ; and I produced 

 a tabulated list in support of my statement. I proposed to account for 

 the distribution of the North American Mollusca which I had thus 

 identified by suggesting that the land and freshwater species might have 

 migrated from Europe to Canada through Northern Asia, and that most 

 of the marine species might have been transported from the arctic seas by 

 the Davis Strait current southwards to Cape Cod, and the remainder from 

 the Mediterranean and eastern coasts of the Atlantic by the Equatorial or 

 some other current in a westerly direction. I renewed my objection to the 

 term ' representative species.' 



There were some unavoidable errors in my list, because I had not 

 sufficient means of making the necessary comparison of American and 

 European specimens on the spot, and some allowance must be conceded 

 for the well-known difference of opinion among naturalists with regard 

 to species and varieties ; but I conscientiously believe that the above com- 

 parative analysis was not far from the mark. All the marine species of 

 Mollusca enumerated in the list were what may be now termed inhabitants 

 of shallow water, in contradistinction to the deep-sea Mollusca which now 

 engage the more special attention of conchologists. 



Since that time, Professor Whiteaves in Canada, and Professor Verrill 

 and Mr. Dall in the United States, have in an admirable and complete 

 manner worked out and published the Mollusca which have for many years 

 past been brought to light by means of the deep-sea explorations made on 

 that side of the North Atlantic. On the European side several equally im- 

 portant expeditions, with a similar object, have been also made during the 

 same period by the British, Norwegian, French, and Italian Governments ; 

 and the Mollusca thns obtained have been published, or are in course of pub- 

 lication. My own papers in the ' Proceedings of the Zoological Society of 

 London ' from 1878 to the present year, on the Mollusca of the Lightning 



