834 



MAJOR G. E. H. BARRETX-HAMILTON AND 



a larger northern with isolated southern colonies, now known to 

 be older in western Europe, a smaller southern, now known to be 

 a recent comer. Such an arrangement shows the relationships 

 most cleai-ly. The earliest known member of the group in Europe 

 is a species of which the fossil and fragmentary remains have 

 been found in the early middle pleistocene brickearth of the 

 Thames at Grays in Essex ; whether this form has any close 

 affinity with any living now it is impossible to say. In the 

 late pleistocene deposits of Britain, such as that filling the 

 Ightham Fissures, and in many of the caves, remains of a 

 large form not certainly distinguishable, with the available 

 materials, from M. agrestis neglectus occur. The Skandinavian 

 agrestis, the Hebridean exsul and macgiUivraii, the pleistocene 

 and recent British neglectus, together probably with the southern 

 French and Swiss levernedii, are all intimately connected forms 

 and may be regarded as subspecies of M. agrestis, and of them 

 macgiUivraii may be counted as the most primitive. At some 

 time since the close of the pleistocene period M. agrestis 

 neglectus has been succeeded in England and the lowlands of 

 Scotland by a smaller, brighter form, which being a newer 

 immigrant, may well be granted specific rank as M. hirtus 

 Bellamy, with M. hirtus hailloni de Selys of France as a 

 subspecies. 



Cranial measurements of Microt-us agrestis. 



