THE FIELD MOUSE 517 



when many adolescent mice are to be found ; mice collected in March 

 or April would probably have given a greater average size for each sex. 

 Six males, collected in East Aberdeenshire by C. S. Burnett between 

 nth and 17th April 1914, with skulls of the " Highland" type, averaged 

 94— 92-2— 21-6— 16- 1, the largest being 99—105—22—16. Aged 

 English individuals probably attain a slightly greater size, althoijgh, 

 no doubt, specimens in which the head and body exceeds 100 mm. 

 are rare. The two largest (both males) caught at Reigate by Ad^ms 

 had the head and body 98, the tail 88 and 86 mm.i Two (male and 

 female) of a series taken at Lowestoft, Suffolk, by Oldfield Thomas 

 were measured as 100 — 94 and 93 — 22-5 and 21-2. Two males collected 

 near Bridgend, Glamorganshire, measured 103 — 85^ — 23, and 106—83 

 —23. A male from Cashel, Tipperary, was measured by De Winton 

 as 103 — 70 (damaged) — 22-5 — 16. 



Distinguishing characters: — Apart from the contrast between 

 reddish upperside and white belly, the large foot is the most infallible 

 point of distinction between any form of Apodemus and other British 

 mice of somewhat similar size ; the peculiarities of the skull and tepth, 

 when available for examination, will always prevent any confusion with 

 other genera. Immature Field Mice in the grey juvenal pelage may 

 easily be confused with House Mice, especially when both are caught 

 together out of doors ; the slender feet and bicoloured tail afford 

 perhaps the best outward means of distinguishing the young Field 

 Mouse. The adult A. sylvaticus is distinguished from A. flavicollis 

 wintoni, the only form with which it is likely to be confused on the 

 British mainland, by its smaller size, duller coloration, and usually by 

 the small size or absence of the pectoral spot. 



(2) A. sylvaticus butei (Hinton). 



1914- A. SYLVATICUS BUTEI, M. A. C. Hinton, Ann. and Mag. Nat. Hist., July 

 1914, 123 ; described from Mountstuart, Bute, Scotland ; type an old male, No. 

 15.5.29.33 of the British Museum collection. 



1913. A. SYLVATICUS SYLVATICUS, G. E. H. Barrett-Hamilton and M. A. C. Hinton, 

 Proc. Zool. Soc, London, 1913, 835. 



Distribution: — The island of Bute. 



Description : — Size nearly as in A. s. sylvaticus, but with relatively 

 much shorter tail and slightly shorter ears. General colour darker, the 

 back and rump being rather heavily clouded with black ; a faint trace 

 of the pectoral spot is frequently present. 



The skull is small, having in adults an average condylo-basal length 

 of 22 mm. instead of 23 mm., as in true sylvaticus ; its relative dimensions 

 show, when compared with those of English skulls of the latter sub- 



' In 95 males measured by Adams the head and body averages about 90 mm., 

 'n 59 females 89-2 mm. ; he found plenty up to 97 or 98 mm. 



