530 PROCEEDINGS OF THE ACADEMY OF [DeC, 



The Boreal (Canadian) areas mapped by Merriam in Kentucky, 

 Tennessee and North Carolina have for mollusca no faunal connection 

 with or resemblance to the Canadian zone fauna of the northern 

 mountains and Canada. There is no evidence that the northern fauna 

 invaded these heights during the Ice Age, but much evidence to the 

 contrary.^ Had such an incursion taken place, it seems hardly con- 

 ceivable that no Vitrina, Pupilla, Vertigo or northern Zonitidm should 

 remain to tell the tale. A certain ill-defined zonal distribution depend- 

 ent on elevation may be traced, the mountain tops having a poorer 

 fauna than the lower levels, with dwarfed races of some species and a 

 few special species ; but the zoological affinities of the forms are in the 

 main with those of the lower coves, not with snails of higher latitudes. 



This illustrates what has been recognized by a few zoologists work- 

 ing in other departments, that transcontinental "life-zones" have no 

 necessary connection with the larger facts of faunal distribution, but 

 define secondary divisions, parallel, so to speak, all over the world. 

 For instance equal zones in the southern Alleghanies and the Rocky 

 Mountains might be spoken of as " physically homologous, ' ' but not 

 faunally so. 



In eastern North America we have, leaving the Floridian tropical 

 element out of the account, two faunas of inland mollusca, developed 

 in diverse areas: (1) the Boreal fauna, consisting of Holarctic species 

 or genera, such as Vitrina, Zonitoides, Enconulus, Acanthinula, Val- 

 lonia, Pupilla, Punctum, Sphyradium, Lymn(ea, etc., which apparently 

 had their rise in the north, and (2) the Appalachian fauna, consisting 

 of forms characteristic of the eastern United States, such as the 

 Mesodon, Triodopsis and Stenotrema groups, Omphalina, Vitrini- 

 zonites, Paravitrea, Gastrodonta, the alternata group of Pyramidula, 

 Helicodiscus, etc. From what we know of the Pliocene land shells, 

 and those of the interglacial and post-glacial Loess, it is clear that these 

 faunas must have been already as distinct at the close of the Pliocene 

 as at present; and in the case of the Appalachian fauna, we have 

 every reason to believe that its ancestors occupied eastern North 

 America during tertiary time, and how much farther back no man can 

 say.^ 



* See in this connection, Pilsbry, Mollusca of the Great Smoky Mountains, 

 Proc A. N. S. Phila., 1900, pp. 110-150, and Walker and Pilsbry, Mollusca of the 

 Mt. Mitchell Region, Proc. A. N. S. Phila., 1902, pp. 413-442. 



" The boreal and southern elements in the east American fauna were fully 

 recognized by Mr. W. G. Binney many years ago. Cf. also Charles C. Adams, 

 Southeastern United States as a centre of geographical distribution of flora and 

 fauna, Biological Bulletin III, pp. 115-131, 1902. 



