DISPERSAL BY MAN. 213 



inland lake near Copenhagen ; that, finally, it had been 

 recorded by M. Charles D'Orbigny as one of the fossils 

 occurring in an upper tertiary deposit in the north of 

 France, and on this ground he (Jeffreys) was not with- 

 out hope that it might be discovered in the correspond- 

 ing strata in this country.^ From various considerations, 

 however, this idea that the creature had always existed 

 in Britain, and had been accidentally overlooked by all 

 our naturalists previously to 1824, seems to me in the 

 highest degree improbable. The " British Conchology " 

 has long been a standard hand-book, and the views of its 

 author have largely influenced the minds of those who 

 have attended to the mollusca, but the very general 

 impression that D. polymorpha is a foreign importation 

 has not been dispelled. There must be good reason for 

 supposing it to have been introduced, otherwise I cannot 

 think that this view, put forward by Mr. Sowerby in 

 1824, would have been endorsed by Gray in 1825, by 

 Fleming in 1828, by Berkeley in 1836, by Alder and 

 Strickland in 1838, by Captain Brown in 1844, by 

 Forbes and Hanley in 1853, as well as by Woodward 

 and nearly all other writers, even including Reeve, 

 Tate, and Harting, whose works were issued sub- 

 sequently to the date of the volume in which Mr. 

 Jeffreys' views were expressed. With regard to Helix 

 carhisiana, H. obvoluta, and Claiisilia rolphii, the three 

 " conspicuous land-shells " mentioned by Jeffreys as 

 clearly indigenous yet unknown to Montagu (who 

 published his " Testacea Britannica " in 1803), it must be 

 * J. G. Jeffreys, " British Conchology;' i. (1862), pp. 47-50. 



