46 LIST OF BRITISH LAND AND FRESHWATER MOLLUSCA. 



and distinguished by 'm.' instead of 'v.' preceding the name. 

 Under this denomination are included all abnormal forms, 

 reversed, scalariform, decollated or distorted. 



The Exclusions from the list are two species of 

 ClausiHa, C. parvula and C. soli da, neither of which has the 

 slightest claim to rank as British. Helix hyb7'ida Poiret also 

 disappears from the list, discarded on account of the confusion 

 which the use of the name entails. For the future it will be 

 more precise to refer specimens to the var. ' Toseolabiata ' or 

 ^f/iscolabiata' of H. nemoralis or II. hortensis, as the case may be. 



Band-variation in Helix nemoralis and H. hor- 

 tensis. — No philosophical plan of treating the numerous 

 variations of these species has yet been propounded, and until 

 such is the case it is deemed the wiser plan to include in the 

 list only variations of size, form, texture, colour of lip and 

 ground-colour. A convenient method or formula, however, 

 exists by which band-variations may be readily and accurately 

 recorded. As all conchologists know, the type form has five 

 bands, each of which is constant in its position on the shell, 

 three of them being always above, and two always below, the 

 periphery. The variation is usually by suppression or by 

 coalescence of one or more of these bands, or both. Number- 

 ing the bands for convenience 1, 2, 3, 4, 5, the uppermost being 

 the first and the lowermost the fifth band, the formula for the 

 type would be written thus: 12345. In the case of the 

 suppression of a band, a cypher (o) is used in lieu of its number, 

 thus — 12045 — signifying that the third band is deficient. The 

 unicolorous form is a case of the suppression of the entire series of 

 bands, and for this the formula is five cyphers, thus — 00000. 

 In the case of coalescence of one or more bands, the numbers 

 standing for the coalesced bands are enclosed within parentheses, 

 e.g. — (12)3(45), which signifies that the first and second bands 

 are fused together, also the fourth and fifth, the third only 

 being free. Any combina'tion of these formulae may be used, 

 as for instance, (12)305 signifies the coalescence of the first 

 and second, and the suppression of the fourth. The black 

 specimens afford an instance of the coalescence of all five 

 bands, for which the formula is written thus — (12345). 



J.C, iv., April, 1S83 



