INTRODUCTION In 1956 I published a revision of a part of the genus Bactra Stephens and ventured to state that "To a diligent student of genital characters Bactra does not present any serious problems" (p. 2). Since that time I had the opportunity to examine an extensive new material; and came to the conclusion that my former statement was unduly optimistic, at least, when applied to the species of the subgenus Bactra Stephens. Contrary to my previous opinion discrimination of several of these species proves to be extremely difficult. Therefore, it seems advisable to anticipate my proposed, more definitive, world-wide revision of the entire genus Bactra by publishing the present preliminary paper, representing the latest results of my examination of the Palaearctic species of the subgenus Bactra. This study is chiefly based on the rich collection of the Zoological Institute of the U.S.S.R. Academy of Sciences, Leningrad, but for a part also on material studied earlier from other sources. The Palaearctic representatives of the subgenus Bactra form a central furfurana group of closely related species, beside a few species which are less closely related. Most of these species are not identifiable without a minute study of the genital characters of the two sexes. It was necessary to describe these structures at some length. I tried to simplify the descriptions as much as possible by introducing some simple terms which are explained in fig. 1a. It was not easy to put slight differences into words; therefore I tried to illustrate the descriptions by as many figures as possible. Not only type specimens are