

PREFACE 



The group of Pulmonate genera familiarly known as Helices, 

 forms an important factor in the land mollusk fauna of every coun- 

 try, in point of numbers exceeding any other group of snails. This 

 numerical and faunal pre-eminence has caused the authors of the 

 MANUAL to devote eight volumes to Helicoid genera, the earlier 

 three (Vol. II to IV) being prepared by Mr. Tryon, the later vol- 

 umes by the writer. 



During the progress of the work it became obvious that the 

 established system of grouping required revision, not alone in the 

 details of many minor divisions, but in those broader principles 

 underlying our conceptions of the entire classification and genealogy 

 of the group. The object of this volume is to formulate in compact 

 form the new classification of Helices, and incidentally to indicate 

 some general principles upon which a new grouping of all land pul- 

 monates must be based. 



In the systematic portion of the work (pp. 1-344) I have 

 attempted to show the main characters of the genera, both in hard 

 and soft anatomy, giving illustrations as copious as the limits of the 

 work would permit ; for while fully pursuaded that, as Darwin has 

 said, naturalists " never read each other's works," I am sure that 

 they look at the pictures illustrating them. In the Introduction the 

 larger groups are defined (p. xxxii) and their probable genealogy 

 suggested (p. xxxi). Finally, the geographic distribution of Helices 

 is discussed with reference to the genesis and migrations of the 

 principal groups, and the origin of modern faunas (p. xxxviii). 



Few will dispute the general proposition that until the systematic 

 classification of a group is placed upon a secure basis, all discussion 

 of the larger questions of geographic and geologic distribution is 

 futile. A sound systematic zoology is at once the key and the test 

 of zoogeographic speculations ; and without this check, zoologist 

 and geologist are alike at the mercy of mere opinion and specula- 

 tion, too often based upon false notions of affinity, or upon a decep- 



