VARIATION IN BANDING. 
101 
Fig. 210. — H. asj>ersa vzcc. Jla7inuca Pic. X K-, 
Scarborough, Yorks., 
Collected by IMr. J. Ray Hardy, 
Showing disintegrated or flammular banding. 
unmistakable traces of 
banding, both in shells and slugs, and transvei'se markings may 
have often arisen from the re- 
aggregation of these spots in the 
direction more or less perpendi- 
cnlar to that in which they were 
primitively present, but it is not 
unlikely that irregularly spotted 
band-like markings indicate ir- 
regularity of action, such as may 
be looked for at the origin of 
such glands, and thus occasionally represent nascent banding and not 
invariably originate from primitively distinct and continuous markings. 
Helix caiiti(um, Helix cartusinna, Helix rufescens, and a few other 
specie.s, although normally uniformly coloured, occasionally exhibit 
banding, which some assert are na.scent, 
but are more probably the vestigial re- 
mains of bands formerly existent; and 
we are thus led to speculate upon the 
probability of these species being at 
one time distinctly banded forms, and 
descended from primitively banded an- 
cestors, without, however, implying that 
the molluscan shell, as originally developed, was not unicolorous. 
The evidences of this banding are rendered easily recognizable by the 
pale peripheral zone, which is, according to my interpretation, the 
intervening area between the upper and lower groups of bands. 
The whitish transverse linear markings, which form the characteristic 
feature of Limnwa jHilustris var. zebra, 
are, I am inclined to believe, the result 
of a certain amount of disintegration of 
the shell substance, which apparently 
takes place at somewhat regular inter- 
vals, owing probably to some periodically 
recurring deficiency in the secretion of 
the protective epidermis. Analogous 
markings from similar causes are some- 
times noticed upon Bythinia tentaculata 
and other species, but this feature is apparently more particularly a 
characteristic of the Limnophysa inhabiting North America. 
Fig. 211. — Helix cantiana var. 
albocincta Ckll., 
Lund, near Osgodby, Yorks., 
Collected by Mr. Wm. Nelson, 
Showing supposed atavistic evi- 
dence of spiral banding. 
Fig. 212. — Litiincea palust) is var. 
zebra Tryon X 2, 
“Swale,” Oakland Co., Mich., U.S.A., 
Collected by hlr. Bryant Walker, 
Showing regular transver.se linear 
markings, perhaps due to disintegra- 
tion of shell substance or defective 
periostraca. 
