_Northern Russia and Siberia._--This vast tract extends from eastern Germany to the Amoor district. It is exceedingly poor in Mollusca, and is chiefly characterised by the gradual disappearance, as we proceed eastward, of European species. There are a few characteristic Siberian Mollusca, closely allied to European forms, and in the extreme east a new element is introduced in the appearance of types which indicate Chinese affinities. The whole district may be regarded as bounded to the south by a line drawn from Lemberg to Moscow, and thence to Perm; passing south of the Ural mountains, it includes the whole basins of the rivers Obi, Yenesei, and Lena, coinciding with the vast mountain ranges which terminate to the north the table-land of central Asia, at the eastern extremity of which it dips sharply southwards, so as to include the Amoor basin and Corea. All the larger Helices are wanting, and no land operculates occur. _Helix arbustorum_ L., _H. nemoralis_ Müll., _H. lapicida_ L., _H. aculeata_ Müll., and _Hyalinia nitidula_ Drap., do not appear to occur east of the Baltic; _Arion fuscus_ Müll., _Helix strigella_ Drap., _Buliminus obscurus_ Müll., _Clausilia laminata_ Mont., _C. bidentata_ Bttg., _C. plicatula_ Drap., _Viviparus fasciatus_ Müll., and _Neritina fluviatilis_ L., do not pass the Urals. In the Obi district (West Siberia) a further batch of European species find their easterly limit. Among these are _Helix hispida_ L., _Bithynia tentaculata_ L., _Vivipara vivipara_ L., _Pisidium amnicum_ Müll., and _Unio tumidus_ Retz. A few distinctly Siberian species now appear, _e.g._ _Ancylus sibiricus_ Gerst., _Valvata sibirica_ Midd., and _Vitrina rugulosa_ Koch. The following are among the European species which reach eastern Siberia: _Hyalinia nitida_ Müll., _Succinea oblonga_ Drap., _Planorbis vortex_ L., _spirorbis_ L., _marginatus_ Drap., _rotundatus_ Poir., _fontanus_ Light., _Valvata piscinalis_ Müll., _Bithynia ventricosa_ Leach, and _Anodonta variabilis_ Drap. Here first occur such characteristic species as _Physa sibirica_ West., _P. aenigma_ West., _Helix pauper_ Gld., _H. Stuxbergi_ West., _H. Nordenskiöldi_ West., _Planorbis borealis_ Lov., _Valvata aliena_ West., _Cyclas nitida_ Cless., and _C. levinodis_ West. In the Amoor district a decided Chinese element makes its appearance in a few hardy forms which have penetrated northward, _e.g._ _Philomycus bilineatus_ Bens., and a few each of the _Fruticicola_ (Chinese) and _Acusta_ groups of _Helix_. Out of 53 species, however, enumerated from this district, as many as 33, belonging to 18 genera, occur also in Great Britain.