[From introduction:]
In my work on Oligochaeta of the Oka River (1927) I came to the conclusion that some of the Oligochaeta limicola may be oonsidered peculiar to rivers alone (potamobiontes)-i. e., they do not occur elsewhere: Propappus volki, Nais behningi, Nais blanci, Potamothrix moldavensis. To this list of potamobiotics I can now add two more species of this family of Aeolosomatidae. These two species inhabit two very characteristic biotops in the river: littoral sand where the current is strong and coarse sand in the middle of the river where the current is likewise strong.