New geographical localities of chromosome forms of southern birch mouse (subtilis group) and description of Sicista severtzovi cimlanica subsp n. (Mammalia, Rodentia) from the middle Don River basin

The chromosome sets were investigated in 12 individuals of the southern bir ch mouse (Sicista genus) group sibtilis from the following geographical poi nts: near Boguchar (southern Voronezh Region) - 1 male, 2n = 18, NF = 28; i n Kalach sands (Volgograd Region) - 1 female, 2n = 2, NF = 44; on the right bank of the Medveditsa river (Volgograd Region)- 1 female, 2n = 26, NF = 4 6; and in Tsimlyansk sands (Rostov Region) - 5 males, 4 females, 2n = 22, N F = 35-36. The specimen from Boguchar was identified as S. severtzovi, that from Kalach sands as S. subtilis, the birch mices from the Medveditsa rive r basin and Tsimlayansk sands are new, previously unknown chromosome forms of the group subtilis. The 22-chromosome form from Tsimlayansk sands are su ggested to be considered as a new subspecies Sicista severtzovi cimlanica. An attempt has been made to describe a pattern of distribution 5 forms of t he group subtilis from the East-European Plain.