PLEISTOCENE GEOLOGY OF THE THAMES VALLEY. 347
Ursus arctos, Linn.
,, ferox, Richd.
Bison bonasus var. priscus, Boj.
Bos taurus var. primigenius, Boj
Cervus elaphus, Linn.
,, giganteus, Blum.
Capreolus caprea, Gray.
Elephas antiquus, Falc.
,, primigenius, Blum.
Rhinoceros antiquitatis, Blum.
,, leptorhinus, Owen.
,, megarhinus, Christol.
Sus scrofa, Linn.
Equus caballus, Linn.
Hippopotamus amphibius, Linn.
Mus sylvaticus, Linn.
Microtus agrestis, Linn.
,, ratticeps, Blas.
,, amphibius, Linn.
,, (Evotomys) glareolus, Schreb.
Castor fiber, Linn.
Sorex vulgaris, Linn.
(b.) Notes on the Species.
Microtus agrestis. Among the Rodentian remains
obtained from the Orsett Road Section are three second upper
molars, several mandibular rami, including one in Mr. J. P.
Johnson's collection, and numerous detached teeth which are
referred to M. agrestis. The only constant dental character
which distinguishes the British Field-vole from the Continental
M. arvalis is the development of three inner angles in the second
upper cheek tooth of the former instead of two in the latter.
This accessory angle of M. agrestis is very small. In dealing
with detached teeth its possession also serves to distinguish
M. agrestis from M. ratticeps. The three teeth from Grays agree
with the British Field-vole in this respect and also in size. We,
therefore, have no hesitation in placing them with this species.
With regard to the mandibular rami and the detached teeth
other than the second upper molar, the evidence is not so
positive. The former plainly belong, from the pattern of the
anterior molars, to either M. agrestis or M. arvalis, while some of