i<P7- Moffat. — The Problems of an Island Fauna. 137 



And some, like the Banded Lemming (Cuuiculus torquatus) 

 and the still more recently identified Scandinavian Lemming 

 {Myodes lemnius), both of which have been added to our list of 

 former Irish animals by Dr. ScharfFs and Mr. Ussher's re- 

 searches since the publication of "The History of the European 

 Fauna," were supposed by the author of that work, when he 

 wrote it, to have entered Europe as part of the great Siberian 

 irruption. If that were so, the Siberian irruption must have 

 reached Ireland in greater force than Dr. Scharff was at first 

 inclined to believe, and I do not know whether he now holds 

 the same view as he held in 1899 as to the place of origin of 

 the Lemmings. At any rate, northern and southern forms 

 alike, and possibly eastern forms too, have died out in Ireland 

 in considerable numbers since a time of which the floors of 

 our caves still tell. It seems, too, that birds like the Hawfinch 

 (now a rare winter visitor) and the Great Spotted Woodpecker 

 (a mere straggler at present to the Irish coast) turned up in 

 the cave-deposits, suggesting, though not exactly proving, 

 that we had a richer bird-fauna in those times than we have 

 now. In short, if the Ice Age was not an exterminating 

 factor, it seems to me that we must find a substitute for it. 

 The dying out of old forms on a continental area can often be 

 explained by the view that newer forms crushed them out in 

 the struggle for existence. But this does not explain how an 

 island fauna comes to be deficient in both sets of species, as 

 we see it in Ireland, where so many of the new forms are ab- 

 sent, through having failed, it is thought, to reach us, and yet 

 the old forms, except a few. have failed to survive to our day. 

 I venture to propound for consideration the question — Do 

 island faunas tend to decrease ? I think they do ; but this, 

 even if admitted to be probable, must not be accepted as proved 

 without very close examination. I do not think that the point 

 has been sufficiently examined. If the rule is for island faunas 

 to tend to decrease, we can never accept the absence of any 

 species from an island as proof that it never reached that 

 island. But I am led to believe that such a rule, or such a 

 tendency, does exist, in the first place, by what seems to be the 

 admitted fact that island faunas are nearly all poor in species 

 compared with the faunas of continental areas of the same 

 dimensions. If we look across Europe and Asia from Great 



