BRITISH FOSSIL SPECIES 133 



Explanation of Fig. 67. 



Microtus sp. (allied tn M. malei). 



Figs. I, 3, 4, 5, 7, 8, 9, 12, 14, 21, 26, from the aevednn Cave. 



Figs. 2, 6, 10, 11, 13, 15-20, 22, 25, 27, 28 and 31, from the Later Middle 

 Terrace deposits of Grayford. 

 Microtia ratticeps K. and Blasius. Clevedon Cave. (Fig. 29.) 

 M. ratticeps. Ightham Fissures. (Fig. 30.) 



abundantly in later Middle Terrace horizons, not only at Grayford 

 and Eritli but in other deposits which I regard as contemporary 

 {e.g., the Clevedon Cave and Banwell Cave). Just how many 

 species should be recognized among the voles listed above as 

 members of the " M. nivalis group " and " M. malei and allies" 

 is difficult to say ; but these forms are strongly marked and 

 especially characteristic of this horizon. I have examined many 

 thousands of Microtine fossils from a great many British deposits, 

 but have never found these peculiar late Middle Terrace forms in 

 association with any species other than those mentioned in the 

 list above. 



d. Ightham Fissure Stage. The species are : — 



'\Dicrostonyx henseli Hinton. 

 *Letmnus lemmus Linnaeus. 

 "fEvotomys harrisoni Hinton. 

 ^Evotomys kennardi Hinton. 

 \Arvicola abbotti Hinton. 

 *Microtus ratticeps Keyserling and Blasius. 

 "^Microtus anglicus Hinton. 

 *Microtus arvalis Pallas. 

 '\Microtus corneri Hinton. 

 Microtus agrestis Linnaeus. 



In deposits of this age Dicrostonyx henseli, Microtus anglicus, 

 M. arvalis, and M. corneri are especially abundant, whereas 

 Lemmus lemmus and Microtus ratticeps are rare. 



Most of the cavern deposits of Britain are intermediate in age 

 between Late Middle Terrace and the Ightham Fissure stages. In 

 these caves one finds Lemmus lemmus and Microtus ratticeps to 

 be more abundant than at Ightham, and Dicrostonyx henseli is 

 frequently replaced by the older form D. gulielmi. Rarely, as 

 at Merlin's Cave, in the Wye Valley, and at the Langwith Cave 

 in Derbyshire, the two species of Dicrostonyx are associated. Of 

 the two species of Evotomys found at Ightham, one {E. harrisoni) 

 is a representative of the living E. glareolus, the other {E. kennardi) 

 is a member of the E. nageri group and therefore probably the 

 forerunner of the peculiar forms which now inhabit some of the 

 smaller islands around the British coast {E. skomerensis, E. 

 ccBsarius, E. alstoni and E. erica). Arvicola abbotti is a widely 



