a 
288 HELIX NEMORALIS. 
character, yet, as in other species, and’in this pre-eminently so, almost every 
specimen combines within itself several of the recognized varietal characters, 
and to fully express the peculiarities of any single shell, it would be neces- 
sary to use two or more of these varietal names, and this act would not be 
a reversion to the old polynomial system of general descriptive nomen- 
clature; but would, on the contrary, constitute a strictly precise and accurate 
terminology. 
Many causes have been suggested to account for the great differences in 
colour and banding—as the nature and colour of the soil, the character 
of the food plants, the nature of the disrict, whether more sunny and 
exposed or sheltered and shady, and whether arid or damp—and it is 
certain that these factors do affect variation, and are a sufficient influence 
to initiate many special modifications. 
The ground colouring in the shell of this species is very variable, and 
would appear to be in an inverse ratio to, and its depth acquired at the 
expense of, the intensity of pigmentation of the banding, as in those shells 
with the most deeply tinted ground the bands, when present, are usually 
few in number, or feeble and rudimentary, while those shells with paler 
ground colouring have often darkly pigmented and well defined bands. 
The suggestion of Dr. Dall that the striping of the shell may conduce 
to concealment, and be therefore protective in the same way as the striping 
of the tiger, zebra, and other animals, is apparently borne out by the 
exhaustive analyses of the shell remains of a large number of “ thrushes’ 
altars” by Rev. E. Adrian Woodruffe-Peacock who, as a result of their 
examination and tabulation established that about Brigg, Lincolnshire, the 
var. libellula 00000 is much more frequently destroyed than other varieties, 
the relics of the single-banded variety being next in abundance, although 
these forms are not the commonest in the districts examined, which leads 
to the inference that these two forms are more readily seen in that district 
than the typically banded shells. 
Distinctly and darkly banded shells are most prevalent in shady and 
umbrageous situations, amidst a luxuriant vegetation, and the absence of 
the banding on the upper surface may possibly be correlated with dwelling 
in elevated, open, bright, and sunny stations. 
The darker and duller shade, frequently seen at the base of the shell 
around the umbilicus, which has been conjectured by Dr. Williams to be 
a discolouration and due to dampness, is more probably an atavistic 
evidence of a former colouring and may be regarded as quite analogous 
with the whitish opacity around the umbilicus of certain Hyaliniw, which 
is a relic of a former more cretaceous shell. 
Though the colour varieties are sporadically found in widely separated 
places, they are often plentiful in restricted districts favourable to their 
evolution and perpetuation; thus the unicolorous brilliant yellow variety is 
said to abound in the open sunny fields about Geneva and elsewhere ; 
and a yellowish variety is recorded by Prof. Howe as prevalent in several 
localities about Lexington, among yellow leaves. A pale form of the 
variety libellula is by far the most abundant and widely dispersed of the 
coloured forms in this country, yet at Aberystwyth and in certain parts 
of the more humid west of England, it becomes dominated by the darker 
and more sombre-coloured var. olivacea, which inhabits moister and more 
shaded localities. 
