VARIATION AND LOCALITY 127 



Helix striata (Draparnauld) 13 is truly polymorphic; and its 

 various forms have been described under various specific names. 

 It abounds in the calcareous hills of Provence and Languedoc, 

 disappearing in the alluvial lowlands and equally in the upper 

 levels at about 800-1,000 m. From this district it extends 

 through regions of similar altitude over a great part of France 

 (details given). 



Locard in his monograph of this group, which he calls col- 

 lectively the group of Helix Heripensis, tabulates 27 distinct 

 named forms. The characteristics in which these forms differ 

 have been reckoned as 17, and as several of these vary in degree 

 of development, the number of modes may be increased to 109. 

 For practical purposes however Coutagne considers that the 

 various developments of 7 characteristics in their several com- 

 binations are enough to express the various forms, and he gives 

 examples of this method of definition. As he observes, though 

 names may be required to define the modes, no one need be 

 alarmed at that, for the same names of modes will be applicable 

 to a great range of distinct species, and the formulae expressing 

 their combinations will replace the varietal names. 



This particular example of polymorphism is but little limited 

 by locality. Occasional colonies present some special physiog- 

 nomy which may in a given place seem almost invariable, though 

 in this very respect the colonies found elsewhere may be highly 

 variable, but such limitations are exceptional for H. striata. 



Some distinct and obvious susceptibilities to the influence 

 of soil and climate are however noticeable. For example on 

 siliceous ground the shells are thinner, while on calcareous soils 

 they are thicker ; similarly those from the Northern districts 

 attain a larger size than those from further South. Moreover 

 those subjected to curtailed development, whether from drought, 

 heat or cold often show a shortening of the spire. In contrast 

 with this case Coutagne describes the varieties of Helix caespitum, 

 which he says are for the most part localised, quoting many il- 

 lustrative cases. 



Another remarkable case in which locality plays a curious 

 part is provided by the two species Helix trochoides and pyra- 



18 As to the synonymy and references see Coutagne, p. 45. 



