510 MURIDiE— APODEMUS 



Arvicola, Apodemus appears to ha;ve died out in Britain during the 

 middle Pleistocene, no trace of the genus being found in the later 

 deposits of the Middle Terrace of the Thames. It then reappeared in 

 the late Pleistocene (Ightham stage) by two forms having close 

 affinities with the living sylvaticus and flavicollis respectively. The 

 sylvaticus-YiVe. form has been discovered in numerous English cave and 

 fissure deposits of late Pleistocene age ; but the remains, although 

 abundant, are not sufficiently perfect to permit of a close comparison 

 with any particular one of the living British members of the group. In 

 Ireland similar fossils have been obtained from the Ballinamintra Cave, 

 Co. Waterford (Adams, Trans. R. Dublin Soc, S. 2, vol. 1., 195, 1881, 

 where they are described as frog bones ; see Scharff, 1 84) ; the caves of 

 Kesh, Co. Sligo, where they were found in all deposits from the super- 

 ficial brown layer to the basal clay (Scharff, 197) ; the Edenvale Caves, 

 Co. Clare, where they were fairly abundant in all the caves, both in 

 upper and lower strata (Scharff, 35) ; and the Newhall and Barntick 

 Caves, Co. Clare, where they were rare and occurred mainly in the 

 upper strata (Scharff, 35). Remains of A. sylvaticus are also common 

 in Holocene alluvial deposits and " submerged forests " in England. 



Description: — In general form the Field Mouse is much like a 

 House Mouse, but differs in its much longer hind legs, larger hind feet 

 and ears, and in its much larger and far more prominent eyes. 



The ears are of a broad ovate form, and extend, when laid forwards, 

 for a short distance beyond the eyes ; they are thinly clad with short 

 hairs ; the antitragus is represented merely by a feeble ridge. The tail 

 is about equal to the head and body in length ; it tapers distally, is 

 somewhat angular in section, and distinctly annulated, there being 

 about 1 50 rings in all ; the tail hairs are short and do not conceal the 

 annulations, though they form a short terminal pencil. The snout is 

 long and very prominent ; the nostrils, separated by an upward 

 continuation of the deep median cleft of the' lip, open obliquely 

 outwards and forwards, and are wider in front than behind ; beneath 

 them the small naked muzzle-pad is bounded by a transverse furrow. 

 In each hand the thumb is a rudimentary tubercle covered by a small 

 nail ; digits 2, 3, and 4 are the longest, 3 is slightly longer, 2 distinctly 

 shorter than 4 ; digit 5 reaches to the base of 4 ; each finger is armed 

 with a small sharp claw and crossed below by deep transverse grooves, 

 of which there are five or six on digit 3 ; the palm is naked and 

 provided with five normally placed pads, of which the two hinder are 

 the largest ; between the pads the skin is irregularly wrinkled. In each 

 foot the hallux extends to the base of digit 2 ; the three middle toes 

 are of nearly equal length, digit 3 being, however, slightly the longest ; 

 digit S reaches distinctly beyond the base of digit 4 ; the toes are 

 grooved transversely below, there being seven or eight grooves on the 

 central digits ; their claws are like those of the fingers. The sole is 



