GENERAL DISCUSSION II 



is one local species, Eidota weyrichi, known only from Sak- 

 halin Island ; * and another, Hclicigona subpersonala, from the 

 valley of the Ud. Three forms of Vivipara (of which two are 

 probably variants of Chinese forms) are the only local species 

 of the vast Amur valley, or drainage, not known from other 

 regions. Nine specially Kamchatkan species have been de- 

 scribed, 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 Penin- 

 sula, and the Asiatic coast north of the Amur and east of the 

 Stanovoi Range, is only eighty-two. 



Of these, thirteen are circumboreal species and twelve are 

 supposed to be locally peculiar. The remainder are distributed 

 as follows : 



Percent 



Europe and west Siberia 55 



Northeast China 22 



Common to America 13 



Erratic species 10 



Of these erratic species a few may be especially mentioned. 

 Margaritana margaritifera, as is well known, is absent from 

 the whole of the great northern central region of North America, 

 though it appears 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. 



Physa 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 Unto is known from east 

 of the Yenisei River of Siberia. 



^n a recent paper Hugh Fulton describes Eulotajilexibilis and E. (Euhadra} 

 fiscina n. sp. as " probably " from Sakhalin Island; but this seems to me very 

 doubtful when we consider the size of these shells and the fact that the warmest 

 part of Sakhalin has a mean annual temperature of only 33.4 F. and for six 

 months of the year the mean is below the freezing point. The shells are more 

 probably from Yesso. 



