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Proceedings of the Royal Society of Edinburgh. [Sess. 
Dicrostonyx, the Arctic Lemming, is undoubtedly represented by a 
few jaws and teeth found in Bed 5 and perhaps also in Bed 3 ; there 
are likewise some limb-bones which in all probability belong to the 
same form. Until the last few years British fossil Lemmings, of the 
D. torquatus type, have generally been referred to that species ; but 
more recently Mr Martin A. C. Hinton and others have shown that 
there are dental and cranial differences among these fossils which 
necessitate a further subdivision, and Mr Hinton has described one of 
these under the name of D. henseli, and, for another, revives the name 
of D. gulielmi of Sanford. Of these species the former is allied to the 
recent B. hudsonius, while the latter more nearly resembles the recent 
B. torquatus. 
One could have wished for better material to indicate the species 
inhabiting the Assynt district in Pleistocene times ; but fortunately there 
are two characteristic upper molars preserved (m 1 and m 2 ), and these show 
the greater development of their posterior angles as in B. torquatus (see 
figure by Barrett Hamilton, Hist. Brit. Mams., part xiv, p. 388, 1913) 
and not the reduced condition seen in the recent D. hudsonius and in the 
fossil D. henseli. Although the characters of the Assynt fossils may not 
be so marked as in the figure just referred to, they agree very closely with 
recent specimens in the British Museum. There are four more or less 
imperfect lower jaws, and only one of these retains the last molar tooth 
(m 3 ), which is said to be characteristic but less distinctly so than the upper 
molars. This hindermost lower molar in our fossil has its anterior angles 
as fully developed as in some of the recent D. torquatus, and the same 
may be said of the second lower molar (m 2 ). It is clear, therefore, that 
this Assynt Lemming belongs to the D. torquatus type as distinguished 
from B. hudsonius. With regard to the size of these Assynt specimens, 
the series of molar teeth in two of them measures 7 - 5 mm. (alveolar length), 
and in a third, probably young jaw, 6 - 5 mm. Among the specimens of B. 
torquatus type now in the British Museum there is much difference of size, 
the alveolar length of the lower molar series varying from 6‘0 mm. to 7*7 
mm. These differences may be due to age, and perhaps to local varieties 
not yet distinguished, but they fall into two groups — those with the molar 
series measuring from 6'0 mm. to 6‘6 mm. in length, and a larger form, two 
specimens, measuring respectively 7*3 mm. and 7*7 mm. There is a re- 
markable agreement, therefore, between the measurements of these recent 
and our fossil specimens. The first of the larger recent forms is from 
N.W. Siberia and the second from Wellington Channel (75° N. 93° W.), that 
is, far to the N.E. of North America. Most of the smaller recent forms are 
