a 
290 HELIX NEMORALIS. 
As in other species, the shell is more liable to be thick and ponderous 
in limestone districts with a mild and equable climate, yet the develop- 
ment of a stout and heavy shell is dependent on the selective action of the 
tissues of the animal, as heavy shells may be secreted in districts in which 
cretaceous material is searce, while thin shells are not uncommon where 
abundance of calcic matters may be present. 
As in all the Pentateeniate species, //elir nemoralis vormally possesses 
five spiral bands, which are constant in their position, three being always 
above the periphery and two always below, but they are subject to a 
marvellous amount of variation, not only due to the total absence of one 
or more of the bands, or their coalescence in diverse combinations, but 
also to the widely differing widths to which each band and each interspace 
is liable, while the more or less irregular pigmentation which results in 
indistinct, irregular, spotted or transparent banding is very striking. 
A convenient method, which is almost universally adopted, of recording 
the variations in the number of the bands . 
present and their mode of fusion, was devised 
many years ago by Herr Georg von Martens, 
by which a distinctive numeral expressive of 
its position on the shell is applied to each of 
the five bands normally present, the uppermost 
band or one nearest the suture being the first, Fic. 345.—Helix nemoralis L., 
and the lowermost or one nearest the umbilicus bowing method of band notation. 
the fifth, the type form with its five bands being indicated with the 
formula 12345. 
A modification was proposed by M. Albin Gras, who suggested that the 
numbering of the bands should commence at the base of the shell and 
that the vowels a, e, i, 9, wu, be used instead of the numerals advocated by 
Herr von Martens. 
The banding when imperfectly developed and showing as a series of 
more or less disconnected spots or blotches is usually represented by a 
colon (:) in place of the numerals which would be used to indicate a 
normal band; the formula ::::: would be used to denote that the five 
bands were irregularly developed. 
Fic. 316. Fic. 347. Fic. 348. Fic. 349. 
Helix nemoralis \.., showing the mode of registering indistinct and deficient 
-? . = Ss . 
banding and the various modes of band diffusion. 
Fic. 346.—Shell showing all the five bands as indistinctly or irregularly developed and usually 
expressed by the formula ::::: 
Fic. 347.—Shell showing the suppression or absence of the third or peripheral band, recorded as 12045. 
Fic. 348.—Shell showing the fusion of the two uppermost and also of the two basal bands, the peri- 
pheral band only being free, and formulated as (12)3(45). 
Fic. 349.—Shell showing band-fusion occurring during growth, and the combination of all the bands 
at the aperture when adult, and represented by the formula [(12)(3(45))]. 
If, however, a band or bands be missing, this is signified by the use of 
a cypher or cyphers in place of the numeral or numerals representing the 
particular band or bands which may be missing ; thus, if the third band 
only be wanting, this would be expressed by the formula 12045, or if all 
the bands are missing, the formula is 00000. 
