The syntypes of the Russian freshwater crayfish, Cambaroides schrenckii (Kessler, 1874) and Cambaroides sachalinensis (Birstein & Winogradow, 1934), that were considered lost, were recently found at the Zoological Institute of the Russian Academy of Sciences, St. Petersburg. Our re-examination has shown that C. sachalinensis is a junior synonym of C. schrenckii. A lectotype of C. schrenckii is designated, and a description is made on the basis of type material and supplemental material recently collected from the Russian Federation. Detailed information on geographic distribution of this species is provided. Morphology and behavior of juveniles, and the position of spermatophores attached to the adult females also are recorded. The phylogenetic position of this genus is evaluated based on these characteristics.