446 Proceedings of the Royal Irish Academy. 



miist have been six sunless montlis every year. Gro-vring still cooler, 

 the climate passed eventually into a phase of extreme cold, -^hen 

 snow and ice extended from the Arctic regions into the centre of 

 Europe and Isorth America. Since that time the cold has again 

 diminished until the present thermal distribution has been reached." 



The late Prof. E. Forbes pointed out, as I have already mentioned 

 (p. 429), that the Lusitanian element in the flora of the south-west of 

 Ireland is the oldest ; and so much was he impressed with that idea, 

 that he held that it must have arrived long before all other British 

 plants. Ve know now that many of the animals belonging to that same 

 migration, e. g. GeomaJacus maculosiis, offer examples, as well as many 

 of the plants, of what is known as " discontinuous distribution.''^ And 

 this alone is a proof of the great antiquity of that Lusitanian element 

 in the Irish fauna and flora. " Discontinuity," says Dr. Wallace (89, 

 p. 69), " will therefore be an indication of antiquity; and the more 

 widely the fragments are scattered, the more ancient we may usually 

 presume the parent to be." Xow, the original home of that fauna 

 and flora is South-western Europe, possibly even some area still 

 further south, of which some of the Atlantic Islands may be the last 

 remnants. The homes of all other components of the British fauna 

 and flora lie further north. Tlie bulk of the Irish fauna and flora, 

 though soutl-.em, is derived, as I stated (p. 429), from South-central or 

 Central Europe. Their distribution is continuous across England, and 

 they are distinctly of more recent origin than the Lusitanian element. 



"We then pass on to the northern or Arctic division of the Irish 

 fauna and flora which came last, and which has scarcely penetrated 

 the island. Hence, there is no doubt that the sequence in the origin 

 of the fauna and flora of Ireland from the temperate to the Arctic 

 agrees perfectly with what we have just learned was the succession 

 of the climates during the more recent geological epochs. "When the 

 climate was mild in Ireland the southern animals and plants migrate d 

 north ; as it gradually became colder they ceased coming north, and 

 species accustomed to more temperate climes took their place, until 

 at last the Arctic ones began to arrive. 



In speaking of the Irish Arctic fauna, we must not, as so many 

 naturalists have done, confuse animals of an Arctic with those of 

 a Siberian origin. It is very important to distinguish these two 

 elements, both of which are present in the faima of Great Britain, 

 though only the fonner has reached Ireland. 



It is now a good many years ago since Mr. Bogdanov (9, p. 26) 

 has brought under our notice that the Arctic animals which have 



