On the Mollusca of Eastern North America. 237 



still be used as a general term for all the forms to which the 

 name has been applied, as the term Zoojihyte was formerly used 

 for such ditferent beings as the Hydrozoa, the Actinozoa, and 

 the Polyzoa. 



EXPLANATION OF PLATE X. 



Callograjytus radicans, Ilopk., natural size. Photo-litliographed from a 

 specimen collected by the author in the Arenig rocks, Ramsey Island, 

 St. David's, South Wales. 



XXXVI. — 77^6 Mollusca of Europe compared loith those of Eas- 

 tern North America. By J. GwYN Jeffreys, F.R.S.* 



After mentionins: that he had dred2:ed last autumn on the 

 coast of New England in a steamer provided by the Govern- 

 ment of the United States, and that he had inspected all the 

 principal collections of Mollusca made in Eastern North 

 America, the author compared the Mollusca of Europe with 

 those of Massachusetts. He estimated the former to contain 

 about 1000 species (viz. 200 land and freshwater, and 800 

 marine), and the latter to contain about 400 species (viz. 110 

 land and freshwater, and 290 marine) ; and he took Mr. 

 Binney's edition of the late Professor Gould's ' Report on the 

 Invertebrata of Massachusetts,' published in 1870, as the 

 standard of comparison. That work gives 401 species, of 

 which Mr. Jeifreys considered 41 to be varieties and the 

 young of other species, leaving 360 apparently distinct species. 

 About 40 species may be added to this number in consequence 

 of the recent researches of Professor Verrill and Mr. Whiteaves 

 on the coast of New England and in the Gulf of St. Lawrence. 

 Mr. Jeifreys identitied 173 out of the 360 Massachusetts 

 species as European, viz. land and fresliAvater 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 he produced a tabulated list of the species in support of 

 his statement. He proposed to account for the distribution of 

 the North-American Mollusca thus identitied, by showing that 

 the land and freshwater species had probably migrated from 

 Europe to Canada through Northern Asia, and that most of 

 the marine species must have been transported from the Arctic 

 seas by Davis's-Strait current southwards to Cape Cod, and 

 the remainder from the Mediterranean and western coasts of 

 the Atlantic by the Gulf-stream in a northerly direction. He 

 renewed his objection to the term " representative species." 



* An abstract of a communication made by the author to the Brighton 

 Meeting of the British Association, and now published at his request. 



