British Fossil Species of Apodemus. 583 



closely these fossils agree with the skulls of equally aged 

 iudividuals of the living British A. f. wintoni : — 



Happaway Wye A.f, tcmtoni 



Cave. Cave. (3 specimens). 



< ^^ : 



Interorbital constriction .... 4-4: 4 4-3 4-5 4*4 



Nasal width 3o ca. 3-3 3-3 3-1 3 



Palatal length 14 2 14-4 13-7 14 13-9 



Diastema 7-5 7-6 7-4 7-3 7-3 



Incisive foramina, length . . ry7 S'O 5*3 5*5 5 



width .. 1-8 2-1 1-9 1-8 1-8 



Rostral breadth 5-4 5'3 5*5 5-3 5-4 



Masseteric plate-width .... 2-9 2-5 2-8 2-6 27 



Cheek-teeth 3-8 39 4 4 3-7 



From the available evidence, it would appear that a flavi- 

 coUis-\\\iQ form first appeared in Britain in Late Pleistocene 

 times, while the syhaticiis group proper had representatives 

 here as far back as the Late Pliocene or Cromerian stage. 

 This would at first sight tend to support Miller's opinion 

 (which I share) that ftavicolUs is really a distinct species 

 from sylvaticus ; but this support may be negatived by the 

 following considerations. 



Like Evotomys, the Microtus agrestis group, and the early 

 species of Arvicola, Apodemus was present in this country in 

 the earlier part of the Middle Terrace stage ; and the forms 

 found in the Grays brick-earth are more or less clearly the 

 descendants of Cromerian ancestors. Some of these old 

 forms appear to have lingered on to the time represented by 

 the Ilford brick-earth. Now, although many small rodent 

 bones and teeth have been collected from the later Middle 

 Terrace deposits of the Thames at Crayford and Erith, no 

 trace of either Apodemus or the other rodents named has been 

 found there ; the place of these forms appears at that time 

 either to have been unoccupied or else to have been taken by 

 quite new forms. Subsequently, in the Late Pleistocene 

 (Ightham stage), Evotomys, the Microtus agrestis and arvalis 

 groups, Arvicola, and the Apodemus sylvaticus group (now 

 including a form like jiavicollis) make a reappearance by 

 forms much more clearly and closely allied to the living 

 species of Western Europe than are those of the older 

 deposits. Such facts caution us against referring the frag- 

 mentary fossils from the Forest Bed and earlier Pleistocene 

 to living species. 



I would take this opportunity of correcting a silly error in 



