Dr. H. A. Pilsbry 



on 



questions of distribution and classification, to give a list of 

 the species described since the beginning of the year 1900, 

 and to record the somewhat extensive synonymy created 

 during that period. 



The work has already reached a point where conclusions of 

 general interest are appearing. The Palaearctic element in 

 the Japanese mollusk-fauna is inconsiderable, but the Oriental 

 element has obviously reached the islands by two routes 

 a northern, vid Sachalin Island, bringing in mainland forms 

 of the Amur valley and northward, ?nd a southern, vid the 

 Loochoo chain and Formosa, and probably from Corea also, 

 though until that peninsula is better known we cannot state 

 this with confidence. Thus, to give one instance, the 

 Japanese group of species commonly referred to the Helicid 

 subgenus Acusta is in reality of dual origin : the species of 

 Hondo and Kiushiu (E. Kieboldiana, Pfr., E. plicosa. Martens*) 

 are related through Eulota despecta of the Loochoo group to 

 E. assimiliSj H. Ad., of Formosa, and to species of Central 

 China. Eulota Iceta, Old., of Hokkaido (Yesso) Island, on 

 the other hand, is allied to species of Northern China and the 

 Amur valley, and really belongs to the subgenus Mastig- 

 eulota. A similarly dual origin can be traced in various 

 other genera. 



The great number of localities explored by Mr. Hirase's 

 collectors permits us now to plot the ranges of many species 

 before known from one locality or from but few places. As 

 the work goes on this will enable us to formulate the lines of 

 migration and the faunal zones or areas of specific and sub- 

 specific differentiation. It is already clear that the islands 

 composing Japan are strikingly unlike most island groups in 

 this that the several islands, as such, are younger than the 

 species of snails living upon them, whereas in most island 

 groups areas of specific and varietal differentiation coincide 

 \vith the geographic limits of the several islands. In other 

 words, the existing species of Japanese snails were in great 

 part differentiated and acquired their present distribution 

 before the islands were separated f. Present knowledge 

 indicates that continuous land extended from the middle 

 Loochoo group to Hokkaido. The Loochoos were first 

 isolated by subsidence ; then Hokkaido was cut off. Hondo, 



* H. plicosa seems to be merely a synonym of despecta, Gray, which 

 occurs in the southern provinces of Kiushiu, as well as in the Loochoo 

 slands. 



f The evidence, so far as supplied by Helices of the Euhadra and 

 Ganesella groups is concerned, has been elaborated in a still unpublished 

 paper by Mr. Addison Gulick and myself. 



