The species of the Chthonius heterodactylus group (Arachnida, Pseudoscorpiones, Chthoniidae) from the eastern Alps and the Carpathians.

The species of the subgenus Chthonius (Chthonius) C.L. Koch, 1843 displaying a sigmoid fixed chelal finger from the Eastern Alps and the Carpathians, assigned to the informal heterodactylus species-group, are revised and a key given for their identification. The following species are present in this area: Chthonius cavernarum Ellingsen, 1909 (Italy, Romania, Slovenia), C. heterodactylus Tömösváry, 1882 (Czech Republic, Hungary, Germany, Poland, Romania, Slovakia, Ukraine), C. hungaricus Mahnert, 1981 (Hungary, Romania, Slovakia), C. lessiniensis Schawaller, 1982 (Italy), C. pusillus Beier, 1947 (Austria, Slovenia) and C. raridentatus Hadži, 1930 (Austria, Croatia, Italy, Slovenia). The following synonymies are proposed: Chthonius diophthalmus Daday, 1889, C. (C.) orthodactylus gracilis Beier, 1935, C. (C.) ksenemani Hadži, 1939 and C. (C.) leruthi Beier, 1939 are junior subjective synonyms of C. heterodactylus Tömösváry, 1882 (n. syn.); C. (C.) pivai Gardini, 1991 is a junior subjective synonym of C. (C.) lessiniensis Schawaller, 1982 (n. syn.); C. (C.) ellingseni Beier, 1939, C. (C.) brandmayri Callaini, 1986 and C. (C.) jalzici Ćurčić, 1988 are junior subjective synonyms of C. (C.) raridentatus Hadži, 1930 (n. syn.). Lectotypes are designated for C. cavernarum Ellingsen, 1909 and C. (C.) ellingseni Beier, 1939. Chthonius (C.) pusillus is newly recorded from Slovenia, C. (C.) hungaricus and Mundochthonius carpaticus Rafalski, 1948 are newly recorded from Romania, and the presence of C. (C.) cavernarum in Italy is confirmed.