
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 
11th 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, although, 
no doubt, specimens in which the head and body exceeds 100 mm. 
are rare. The two largest (both males) caught at Reigate by Adams 
had the head and body 98, the tail 88 and 86 mm! 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 Afodemus and other British 
mice of somewhat similar size; the peculiarities of the skull and teeth, 
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 
wintonz, 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 butec (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., asin true sy/vaticus ; its relative dimensions 
show, when compared with those of English skulls of the latter sub- 
1 In 95 males measured by Adams the head and body averages about 90 mm., 
in 59 females 89-2 mm. ; he found plenty up to 97 or 98 mm. 
