72 The Irish Naturalist. May, 



that many species of mollusca are found in older strata in 

 England than in (lermany, and that a good many British 

 species, both recent and fossil, are unknown in Germany in 

 either a fossil or recent condition— considerations which 

 appear fatal to tlu"s theory, even without appeal to much 

 evidence derived from other groups w^hich is equally opposed 

 to it. The " (ilacial extermination theory " aftects us more 

 nearly, since we are compelled to admit the strength of the 

 local geological evidence for a xQvy widespread destruction 

 of the fauna and flora during the Ice Age, however much 

 we may believe that the zoological and botanical evidence 

 points in an opposite direction. Of the man}^ difficulties 

 \\'hich the naturalist encounters in this theory, our authors 

 lay special stress on the very shadowy character of the post- 

 Glacial land-bridge which it postulates, and consider that even 

 its assumed existence will not account for the presence of 

 such forms as Geornalacus maculosus, Limnaea involitta, and 

 L. praetenuis ; while the absence from Ireland of snakes, 

 voles, etc., is equally difficult to reconcile with the theory 

 of a post-Glacial connection. Admitting its absence, we 

 might, like Clement Reid, invoke winds, currents and birds 

 to sow our country with seed from which the present flora 

 arose (though in the wildest flights of imagination I cannot 

 conceive it) ; but what about the Irish post-Glacial and 

 existing mammalian fauna ? — not to mention sensitive and 

 delicate invertebrates quite unsuited to aerial or marine 

 adventures. 



Our authors, then, reject what we may call, from its 

 latest and most able exponent, the Clement Reid hypothesis 

 — very properly, to my mind. For, in addition to the 

 difficulties offered by such considerations as the above, I feel 

 compelled to traverse much of the positive evidence which 

 that writer brings forward in support of his contentions. He 

 states, for instance, that a study of the habitats and range 

 oi the Lusitanian plants convinces him that they are very 

 recent arrivals, rapidly spreading from local centres of 

 dispersal which can still be fixed. I believe that an un- 

 biassed study of the question will lead the observer to a 

 precisely opposite conclusion. He quotes the " small- 

 seededness " of the same group as strong evidence of the 



