366 POPULAR SCIENCE MONTHLY. 



There is one local species, Eulota iveyrichi, known only from Sakhalin 

 Island; and another, Ilelicigona subpersonata from the valley of the 

 Ud. Three forms of Vivipara (of which two are probably variants 

 of Chinese forms) are the only exclusively local species of the vast 

 Amur Valley, or drainage, not known from other regions. Nine 

 specially Kamchatkan species have been described, but about half of 

 them are doubtfully distinct. 



The total number of land and fresh-water mollusks known from 

 the Amurland, Sakhalin, Kamchatka, the Chukchi peninsula, and the 

 Asiatic coast north of the Amur and east of the Stanovoi range, is 

 only eighty-one. Of these thirteen are circumboreal species, and 

 twelve are supposed to be locally peculiar. Of the remainder 



Europe and West Siberia contribute 55 per cent. 



Northeast China contributes 22 " 



In common with America there is 13 



Erratic species 10 " 



Of these erratic species a few may be especially mentioned. Mar- 

 garitana margaritifera, as is well known, is absent from the whole of 

 the great northern central region of North America, though it ap- 

 pears in the Lower Saskatchewan, the sources of the Missouri and in 

 eastern Canada, while on the Pacific it ascends at least to latitude 

 56° N. In eastern Asia it is known from Kamchatka, Sakhalin 

 Island, the upper portion of the Amur basin, and southern Mongolia — 

 but I find no authoritative record of it thence westward to Northern 

 and Middle Europe. Schrenck did not find it on the lower Amur. 



Pliisa fontinalis is reported from the upper Amur and (in a duck's 

 crop) the desert of Dauria, but is not known from Siberia proper, 

 though common in Europe. There is an entire absence of typical 

 Physa throughout East Siberia, so far as reported; and only one species 

 of Ancylus or Vnio is known from east of the Yenisei river of Siberia. 



Aplexa hypnorum is known from Northern Europe, Western 

 Siberia and the Chukchi peninsula, but has not been reported from 

 Eastern Siberia, or the Amur, though abundant in Alaska, and reach- 

 ing on the Taimyr peninsula to 73° 30' North Latitude. 



Zoogenites harpa is known from Northeastern Scandinavia in 

 Europe; from Northeastern America, the Hudson Bay territory and 

 Southeastern Alaska, in America; but in Siberia it is recorded only 

 from the easternmost margin; the Chukchi peninsula, Bering Island, 

 Kamchatka and the lower Amur. These singularities of distribution 

 must await much more extended knowledge before they can be ade- 

 quately discussed, but it is believed that to some extent they are due 

 to the transgression of the sea, or of glacial ice, over part of the area 

 in which a species might naturally be expected to occur, thus delaying 

 the occupation of the entire region by the species concerned. 



