4 HELICID^E. 



of some volumes of this work several of them for Helix alone 

 the usual synopsis of genera is omitted (it may be found in 

 Structural and Systematic Conchology, iii, 28-58), and I proceed 

 at once to the consideration of the 



Genus HELIX, Linureus. 



Shell of variable form, orbicular, convex, planorboid, trochi- 

 form, subturriculated or short bulimiform (monstrosities sinis- 

 tral, or with whorls more or less uncoiled), smooth, rugose, 

 striate, ribbed, tuberculate, sometimes pilose, often variegated 

 in color ; the aperture oblique, oval or semilunar. with or 

 without teeth on the interior of the lip, or parietal wall or colu- 

 inella ; the lip usually reflected, sometimes internally thickened, 

 sometimes simple and sharp ; umbilicus varying from covered 

 to widely open. 



No more precise diagnosis can be given of a genus in which 

 the conchological features vary so much as they do in Helix. 

 Albers, Beck, Swainson, Ferussac, the brothers Adams, Pfeiffer, 

 and many others, have proposed a great number of groups rank- 

 ing from sections merely, to genera, but which agree in pos- 

 sessing but little individualit}* in a systematic, although highly 

 important in a developmental aspect. In fact, the species in 

 these groups very generally indicate more strongly here than in 

 any other branch of Conchology, both by their general facies 

 and by the territory peopled by them, their common ancestry. 

 This is possibly the effect of a more recent appearance and a 

 more rapid development than in the marine groups of mollusks, 

 the extinct forms extending no further back than the cretaceous 

 period in Europe and the somewhat later Laramie in the United 

 States, and altogether very few in number, whilst the number of 

 species now living is not far from four thousand ; indeed, it is 

 not improbable that much of the differentiation has taken place 

 within the historic period. 



The number of species of Helix, although considerably reduced 

 in late years by the elimination of the genera comprised in the 

 family Zonitidre, still remains so large that further disintegra- 

 tion would be very desirable, were it practicable ; unfortunately, 

 no divisions have been proposed having the distinctive charac- 

 ters usually assigned to genera and subgenera. As a mere 



