GEOGRAPHIC DISTRIBUTION. XXXIX 



find that the life areas defined by mollusks and those based on the 

 vertebrates named, correspond in all respects ; although the much 

 greater time limit in the case of mollusks to some extent offsets their 

 slower movements. The same factor of greater antiquity introduces 

 another disturbing quantity into the equation ; for land mollusks 

 have been able to take advantage of early continental and insular 

 connections which no longer existed when the modern orders of pla- 

 cental mammals came upon the stage. 



In the following pages, the distribution of the Helices will be dis- 

 cussed in order of groups. It will readily be understood that the 

 hypotheses offered, whether borrowed or original, are simply sugges- 

 tions, subject to such changes as the study of other groups or of 

 palaeontology demands, or to complete rejection. They are based, 

 however, on a careful consideration of the facts now known, with 

 regard to land snails generally; and are, I trust, fair inferences 

 from these facts. 



Endodontidce. As will be seen in the systematic part of this work, 

 this family is intermediate between Zonitidce and Helicidce in its 

 characters, and it is decidedly less specialized than either. While it 

 may not be in the direct line of descent of these two families, it is 

 certainly nearer than either of the others to the common ancestor of 

 the three, as is shown by its unspecialized jaw, teeth, genitalia and 

 shell. Palaeontology has yet given but little to the history of the 

 group, but that little is significant; the Carboniferous of Nova Sco- 

 tia has afforded a small Helicoid described as Zonites priscus Cpr., 

 which in form and ribbed-striate sculpture can only be compared to 

 such Endodontidce as Pyramidula or Charopa. In my opinion this 

 species is to be regarded as the oldest form of Helicoid yet known, 

 and as a probable member of the genus Pyramidula. 



Agreeing with this view of the antiquity of the group is the fact 

 that the Endodontidce have a wider geographic ranpe now than 

 either Helicidce or Zonitidce, inhabiting the entire Holarctic realm, 

 the southern extremities of S. America and Africa, Australo-Zea- 

 landic land, and almost all oceanic islands of the entire globe. 

 Upon the continents they are very scarce or absent in the tropics, 

 probably from the competition of numerous newer groups ; and it 

 is mainly in island faunas, where they do not compete with true 

 Helicidce, that snails of this family abound. The presence of very 

 similar forms in southern South America and Tasmania and New 

 Zealand, has been accounted for by the hypothesis of a former more 



