TABLE OF DISTRIBUTION. 315 



Geology, that any reliable information with respect to 

 the present range of the European MoUusca cannot fail 

 to assist in the elucidation of this question ; but I would 

 again venture to express an earnest hope that, until suffi- 

 cient data have been collected, no more theories, crude 

 although plausible, may be put forth. It may be said that 

 they are easily made, and that by their discussion some 

 useful results are obtained ; but it must not be forgotten 

 that the eyes of our scientific compeers in Europe are 

 upon us, and that our reputation for accuracy, as well 

 as our position as naturalists, may be compromised if 

 we erect a fine superstructure on a foundation of sand, 

 instead of digging patiently, but steadily, until we reach 

 the solid rock. 



I propose to show, in the following Table, 



1st, All the species of land and freshwater Mollusca 

 now living in the British Isles, arranged in the natural 

 order of their classification. 



2ndly, The extra-British distribution of any of these 

 species, north of a line dra\\Ti in the meridian of Bordeaux, 

 which maybe assumed as an arbitrary point of demarca- 

 tion between the two extremes of climate in Europe ^'. 

 These species may be termed " northern '' forms. 



3rdly, The like distribution, of any of the species com- 

 prised in the first category, south of the same line — being 

 therefore "southern " forms. 



And 4thly, The occuiTence of any of the above-men- 

 tioned species in a subfossil state, in the upper tertiary 

 strata of this country. With respect to the term " Upper 

 Tertiaries,^^ Mr. Prestwich has kindly suppHed me with 

 the following definition : — 



"By our upper Tertiaries I should be disposed to 



* Draparnaud, in his "Tableau des Mollusques," proposed nearly the 

 same line of division betweeii the North and South of France, the latter 

 being tlie olive-district. 



p2 



