THE BANK MOUSE 411 



of 81 ; another.of 85 contained two embryos. At about 85 adult pelage 

 is assumed, and from 90 upwards the majority are sexually mature. 

 Many grow on to a much greater size, 

 and, in exceptional cases, females have 

 been found to be sexually immature at <^5^ — fni 

 97 or 99- It is not clear whether dimen- 

 sions exceeding 100 are abnormal, or 

 whether every individual would reach 

 that size if not previously destroyed. 

 Apparently they continue to grow for 

 a long time, and Millais finds that all 



Microti improve considerably in colour ^'^ "'^ ~ 



and size until they are two years old. 



There is nothing to show that the sexes ^ ^ 



differ constantly in size. Fig. 63.-Cheek-Teeth of Evotomys 



SkuU: — Condylo-basal length, 21-2 skomerensis (a, right upper; B, left 



to 24-2; breadth at zygomata, 12-2 to 1°™": 7 times life size). (Drawn by 



... I-. 1 i • i- ^ ^ M. A. C. Hinton.) 



14; at mter-orbital constriction, 3-0 to ' 



4'2 ; at occiput, 10-7 to 1 1-8 ; median occipital depth, 5-8 to 6-4 ; greatest 

 length of nasals, 5-6 to 7-4; of diastema, 5-6 to 7-2 ; of mandible, i2-8 

 to I4'8 ; of maxillary tooth-row, 4-8 to 5-6 ; of mandibular tooth-row, 

 4-8 to 5-4. 



Distingmshing characters : — As between mice of this genus and 

 others of similar size, the hairy, bicoloured tail is probably the 

 most distinctive external character. Its length, about half that 

 of the head and body, is greater than that of any Microius, 

 shorter than that of any member of the sub-family Murines. In the 

 skull the simple palate, rooted cheek-teeth with rounded salient angles, 

 and transversely open triangles of ;«., are diagnostic. The characters 

 of the other species of Evotomys are given under their special headings. 



The Bank Mouse ^ is not specialised by its structure 

 for a narrow type of existence. Its habits are, therefore, of 

 comparatively wide range, but not strikingly peculiar in any 

 particular direction. It may be found in all the situations 

 ordinarily affected by Grass Mice or Field Mice, without, how- 

 ever, adopting the extreme r6le of either. In demeanour and 

 activity it is quite intermediate, being less fossorial, but much 

 more rapid and agile in all its movements, than the Grass 



■ Of earlier original accounts that of E. R. Alston, in Bell's second edition, 

 usually, but incorrectly attributed to Bell himself, is, considering the date, 1874, 

 perhaps the best. Other original accounts are those of G. T. Rope, Science Gossip, 

 July 1886, 155-7 ; and of Douglas English, Some Smaller British Mammals (undated). 



