THE ISLAY SHREW 27, 
SKULL MEASUREMENTS IN MILLIMETRES :— 



S. a. castaneus. S. grantit. 
15 Specimens from Jura, 
Mull, Bute, Great Cum- 12 Specimens. 
brae, and Arran. 
Maximum. Minimum, Maximum. Minimum. 
Condylo- basal length . . 19°0 Urey 19°3 18-2 
Malar breadth . 3 = 5 63 4°8 55 62 
Interorbital breadth 5 5 3-9 3:3 3°8 3°5 
Width of brain-case . . . 9°6 89 9°6 89 
Depth of brain-case . 3 = 52 4°7 52 5-0 
Maxillary tooth-row . . 8-2 76 84 78 
pttoms. = 2 = > 45 4°2 46 43 
Mandible . 6 c . . 9°8 9°0 9°9 9°3 







The skull agrees in form and size with that of S. a. castaneus, but 
attains rather larger dimensions than skulls of the latter species 
from northern Britain and the Inner Hebrides. 
The teeth agree in form with those of S. avaneus, but there is 
no trace of pigment upon the hypocones of the upper cheek-teeth, 
nor on the protocone of 73. The posterior unicuspid tooth 2 tends 
to disappear, as shown by the following statistics :— 
#2 present on both sides of the jaw, 7 individuals, or 43-7 per cent. 
;, absent from one side - 4 i 2 
53 both sides___,, 5 _ 
5 ” 
1-3 ” 
> bt 
When 72 is absent the four remaining unicuspid teeth appear to be 
somewhat enlarged. 
Status :—By colour and dentition S. gvantiz is clearly differentiated 
from all European members of the genus Sorex. Some of these, such 
as S. avaneus araneus and a. tetragonurus, have the back as dark, but 
none shows the conspicuously contrasted sides. S. gvrantiz may 
perhaps be regarded as an insular development from S. a. castaneus. 
It has maintained or acquired slightly larger dimensions than has 
the latter in the more northern parts of its range. The Islay Shrew 
has developed a peculiar colour pattern, and is now well on its way 
to reduce the number of the unicuspid teeth, perhaps because of a 
tendency to enlarge the anterior members of the series. The Shrew 
inhabiting Jura, while definitely a form of S. avaneus, is geographically 
and morphologically the connecting link between S. a. castaneus and 
S. grantit,; it has the small size and the dental characters of northern 
