Lataste has already shown, the terrestris and amphibius of Linnaeus are the same
animal. ‘ The Mus amphibius of Linnaeus,’ he remarks, ‘ is nothing more than a
figment of the imagination based on Ray’s misconception that there is a large
aquatic Vole with webbed feet.’ According to this argument the species should be
called Microtus terrestris, Linn., or, if we accept Mr. Miller’s sub-genus, A rvico la
terrestris, Linn. For the present, however, I prefer to retain the name
amphibius.
Characters.—This, the largest of our Voles, differs from the other species
inhabiting Britain in possessing a moderately long tail. The fur is long and
thick, and generally has an external appearance of grey brown. I f examined
closely the fur of the upper parts is pure grey in the hidden portions and a
mixture of pale yellowish brown and black hairs on the lower parts; the outer
hairs are generally sandy brown. Sometimes a reddish tinge is noticeable
over the whole coat in winter, especially in the case of southern specimens.
The vibrissae are black with whitish ends. The eyes are black. The hind feet
are sparsely haired and covered with fine yellowish-grey hairs on the upper
surface. The tail is covered with black hairs and often has a pure white
tip. The first upper molar has five and the second and third have four
prismatic spaces, whilst in the lower jaw the first molar has seven spaces, the
second five, and the third three spaces. In the case of the first lower molar
the first three spaces are often imperfectly separated. The incisor teeth are
brownish yellow.
The limbs are somewhat small compared with the body, which is short and
thickset. The ears are short and buried in the fu r: they are covered with sparse
hairs externally and the aperture of the internal ear is capable of being closed by
an ‘ operculum.’ The claws are yellow with lines of purple on the upper
surface.
The presence of musk glands is peculiar to this sub-genus, and these are
described by Miller in the following manner: ‘ The species of A rvico la are
provided with a large musk gland on each side of the abdomen. These glands lie
immediately in front of the hind legs. They are regularly oval in outline, the
long axis parallel with the long axis of the body. The surface, which is slightly
raised above that of the surrounding skin, is closely and irregularly wrinkled, and
has much of the appearance of very fine honeycombed tripe. Each gland bears a
sprinkling of fine hairs much shorter than the fur, but at first sight appears to be
naked.’