EVOTOMYS 403 
The posterior loop may be simple or complicated by the 
presence of extra infolds — generally a shallow antero- 
external and a deep internal’—the 
latter extending across the tooth 
nearly to the enamel of the outer 
side; there are many intermediate 
conditions, but in the simplest form 
there are on each side three salient 
angles and two infolds; in the most 
complicated form there are four or 
five salient angles and four infolds on 
each side. Fic. 62.—RIGHT CHEEK-TEETH 
In MN, the posterior transverse loop OF Evoiomys glareolus (A, upper ; 
is preceded by two outer and three hae GLO EW ay aes 
inner more or less closed triangles ; 
the tooth has thus four outer and four or five inner salient 
angles; the third inner triangle opens more or less broadly 
into the short anterior loop, which presents externally a well- 
marked salient angle, while its inner border may form another 
salient angle or may be rounded and only slightly salient. 
m, and m, are composed each of three more or less trans- 
verse dentine-loops, giving rise to six salient angles and four 
infolds; those of the outer side are poorly developed, espe- 
cially in the 7, in which when well-worn the anterior angle 
and infold may be absent. The first and second loops of 72. 
and the second loop of ms, especially the former, may be 
partially or completely divided into triangles. 
The sub-genera Craseomys and Phaulomys indicate advanced 
specialisation, but seem to be rather of ‘‘ group” than of higher 
value (see Anderson, Ann. and Mag. Nat. Hist., Oct. 1909, 
317, and May 1905, 493). 
The genus contains a number of species, of circumpolar 
distribution, from the shores of the Polar Sea (introduced in 
Bering Island) through arctic, boreal, transitional, and some- 
times subtropical zones, but absent from Greenland, the 
islands of the Polar Sea, Newfoundland, Spitzbergen, Novaya 
Zemlya, and Iceland. South it ranges in North America to 

1 This is variably developed in the different species; it is present in about 25 
per cent. of Z. g. britannicus. 
