SUB-VARIETIES. 
61 
typical form, and therefore possess a certain value and importance, 
as enabling or as.sisting us to fix the varietal status, and refer to 
their appropriate species, the doubtful and abnormal forms occasion- 
ally met with ; but the relative importance of the varietal or sub- 
varietal modifications cannot always be measured in accordance with 
the more or less readily discernible nature of the differences exhibited. 
The conspicuous differences in the variations of the banding of the 
shells of Helix nemm'alis, Helix hortensis and other Pentateniate 
.species, although palpable and unmistakeable to the most unpractised 
eye, are relatively of very minor importance, in comparison with the 
more subtle variations in form or character, which may often require 
a trained eye and judgment to discern and appreciate; the variety 
lutea of Helix hortensis stidctly speaking refers only to the bright 
yellow shells, though generally understood to include all yellow forms, 
and tliese can and have been sub-divided and named by different 
authors, the greenish-yellow form has received the names of fiaro- 
virens from Picard and flaco-viridis from Kickx, the greyish-yellow 
forms have been styled griseo-lutea by Esmark, and all the innumer- 
able band modifications whether of number, color, or arrangement 
are sub-varieties or modifications of the more important varieties. 
The Depressed and Conoid forms of species usually somewhat sub- 
globose in shape, results from a more or le.ss rapid deflection of the 
whorls ; if, in the process of growth, the whorls descend more quickly 
than usual, we have as a result a more produced and elongated form 
of shell with a smaller aperture, as in Helix nemoralis var. conica 
Fig. 132. —A Conical variety of a Sub- 
globose Univalve. 
Helix nonoralis var. conica Pascal, 
Seacroft, near Leeds. 
Fig, 1.33. — A Depressed variety of a Sub- 
globose Univalve. 
Helix nemoralis var, planospira Picard, 
Frutigen, S\vitzerland. 
Pascal. Inversely, if the descending growth of the whorls be less 
decisive than normal, then we have a depressed and more or less 
planorbiform shell, as in Helix nemonilis var. planospira Picard, and 
this form of modification usually results by correlation of growth in a 
shell of greater diameter than ordinary with a more expanded aperture. 
