190 ARION ATER. 
Generally speaking, its distribution has been stated by the late Prof, 
Von Martens to range with that of the oak, about the isotherm of 42° 
Fahrenheit, but it is probable that this statement now needs revision, the 
range of this species apparently extending beyond what was previously 
known, while it has also been recorded as ascending the Pyrennean Moun- 
tains to a height of more than 6,000 feet. 
In Norway, the red variety only reaches as far as the fiftieth parallel, but 
the black variety has been noted to extend to 68° north lat., while the var. 
alba is recorded from 'Trémsdalen, 69° 50’, its occurrence supporting 
Gredler’s view that albinism is often an indication that the species has 
reached the limit of its geographic or vertical range. 
It is known to occur in Germany, Belgium, Holland, France, Austro- 
Hungary, Switzerland, Denmark, Norway, Sweden, North Italy, Spain, 
Portugal, and the British Isles. 
It has also been recorded for Russia, from the Ukraine, Finland, the 
Baltie provinces, and elsewhere, by Kaleniezenko, Nadjeschin, Kawall, and 
other writers, but, according to Simroth, in every case erroneously. 
Geographical Distribution 
of 
Arion ater (L.). 
MMMM Recorded Distribution. 
| Probable Range. 
Fic. 206. 
BRITISH ISLES. 
In the British Isles this species is universally distributed, being found 
in all the one hundred and forty-nine comital and vice-comital districts 
into which the country has been divided, and has even been collected by 
Mr. W. E. Clarke on the Flannan Isles, the most westerly of the Outer 
Hebridean islets. ‘This comprehensive survey of specimens has emphasized 
the dull, dark forms as the characteristic colouring in these islands: the 
brighter coloured varieties being more plentiful in the southern counties, 
and during warm dry summers, while the greater prevalence of the fasciate 
or juvenile colouring in Ireland shows the more primitive character of the 
fauna and its greater remoteness from the theatre of the most evolutionary 
activity. 
