Clare Island Survey — Mammalia. 17 5 



In spite of its wide distribution, comparatively few subspecies or local forms 

 have been described, so that it appears to be a form of low plasticity — so 

 lacking in plasticity in fact that it is represented in North America by a very 

 closely allied form, S. personatus. 



Its wide distribution, its lack of plasticity, and the fact that the adult 

 wears a pelage corresponding to that of the juvenile Common Shrew point to 

 an ancient and primitive species. Its comparative rarity on the mainland of 

 Great Britain might be accounted for by its having been displaced by the 

 larger Common Shrew ; but this latter suggestion can only be regarded as 

 supposition, and is not borne out by the facts at present available regarding 

 its history in past geological times ; for it is known as a fossil in Britain 

 only from the latest pleistocene deposits (Ightham fissures). All other remains 

 of shrews belong to distinct species. 



A fact which points to its having been a comparatively recent immigrant to 

 western Europe is that, although present in Skandinavia, it is not found in 

 Spain, having apparently not had time to cross the barrier formed by the 

 Pyrenees. 



This fact, together with its smaller size, makes it necessary to note that 

 it is just the kind of mammal that might most easily have been introduced 

 to the numerous islets where it is now found. On the other hand, it is 

 extremely hardy, and capable of standing considerable quantities of frost and 

 snow, and, although it is very voracious, its minute size and unfastidious 

 appetite enable it to subsist in cold countries where larger animals would 

 starve. 



There is, then, nothing to prevent this species having been one of the 

 oldest members of the Irish fauna, but there is no evidence to show in the 

 slightest degree how long it may have been so. But had it survived the 

 Glacial Period 1 in Clare Island, such long isolation in the narrow confines of 

 a small island might have been expected to have caused local differentiation 

 of at least subspecific value, even in an animal of admittedly low plasticity. 



Wood Mice (genus Apodemus), although just the mammals that one would 

 expect to find accompanying the Pygmy Shrew on Clare Island, present some 

 totally different characteristics. In the first place, they are even more 

 widely distributed, being found in Spain, north Africa, and on many of the 

 islands of the Mediterranean, such as Corsica and Sicily. In the north they 

 are common in southern and central Skandinavia, and in Britain they have 



1 The term " Glacial Period " is not here used in its older sense as indicating a long period of 

 variable frigidity removed from the present epoch by an immense gap of time. It is here applied 

 merely to a period of glaeiation which occurred in quite recent geological times somewhere about the 

 end, if not at the actual termination, of the pleistocene Period. 



