The genus Hystrichopsylla is Holarctic in distribution; its species include the largest known fleas. Only a few of the species exhibit marked host preferences. H. talpae (Curtis), the type of the genus, occurs through much of Europe and Asia, where the favoured hosts are insectivores and small rodents. It differs from all other known species chiefly in the presence of true combs of long, pigmented spines on abdominal terga II to IV (Fig. 1). Because of the differences, Ioff and Scalon (1950, in Ioff and Scalon et al., p. 273) proposed the subgenus Hystroceras (type, H. satunini Wagn.) to contain a group of Palaearctic species (satunini Wagn., microti Scalon, and nicolai Scalon) that have the abdominal combs reduced to series of apical spinelets (Fig. 2); this taxon would include all the known Nearctic species of Hystrichopsylla. Ioff and Scalon considered Typhloceras Wagn., known only from the Palaearctic region, a third subgenus, but this interpretation will probably not be generally followed.