348 PLEISTOCENE GEOLOGY OF THE THAMES VALLEY.
the upper teeth may also represent M. ratticeps, Yet seeing that
M. arvalis is unknown at present from Grays by any indubitable
specimen, and that M. ratticeps is very rare at this locality, we
feel justified in referring these remains provisionally at all events
to M. agrestis. The species has not previously been positively
recorded from the Pleistocene of the Thames Valley. It is
known, however, from other Pleistocene deposits.
Microtus ratticeps. We have in our collection from
Grays three specimens of the third upper molar of a small vole.
They present four well developed external angles such as
characterize the corresponding tooth in the figure of the denti-
tion of the typical M. ratticeps given by Prof. Blasius (II.,
p. 366, fig. 201). Although this tooth is variable in M. ratticeps,
sometimes agreeing with M. arvalis and M. agrestis in having only
three external angles, still we know of no vole whose variations
agree in this respect with the typical form M. ratticeps. We,
therefore, have little doubt of the correctness of referring these
specimens to this form, and it is to be hoped that the still
more characteristic anterior lower molar will be found at Grays.
The species is known from the Pleistocene of Crayford and
Erith and from other strata of a similar age.
Microtus amphibius. The remains referred to M.
amphibius from the Orsett Road Section include a left ramus
with the anterior and second molars and numerous detached
teeth. They all agree with recent examples in the pattern of
the crowns. In size, however, they differ ; nearly all the
examples that we have obtained from Grays are small, approach-
ing M. intermedius in this respect, but as none of the teeth are
fanged it is clear that they represent a local and small race of
M. amphibius.
The Water-vole has long been known from the deposits
of Grays and other places in the Thames Valley, and has
likewise been obtained from many other Pleistocene beds. It is
somewhat doubtful whether it occurs in the Norfolk Forest
Bed.
Microtus (Evotomys) glareolus. A first upper cheek
tooth of the left side from the Orsett Road Section, in our
possession, agrees with the corresponding teeth of recent
examples of the Bank-vole in pattern, size, and the possession of