It cannot be said that any satisfactory division of the Tetrastichini has yet been proposed. With the exception of one or two easily recognised groups like Melittobia, Westw., Crataepus, Först., and Hyperteles. Först., the genera are ill-defined, and this is specially the case with Tetrastichus, Hal., and its immediate allies. It has become evident that the mesonotal furrows or impressed lines have not the value for diagnosis that many writers have assigned to them. Recently Kurdjumov (Revue Russe d'Entomologie, xiii, p. 246, 1913) has separated Tetrastichus from Geniocerus, Ratz., by the chaetotaxy of the submarginal, assigning to the former genus those species which have one, and to the latter, species with more than one bristle in this position. Such a division, I believe to be unnatural, as it is certainly inconvenient.* In the following descriptions I have included one species in Tetrastichus though it has more than one bristle on the submarginal. I think it impossible, in the present state of our knowledge of the Tetrastichines, to say what characters are of basal importance. For grouping species, the funicle (shape, segments and chaetotaxy), the position of the scrobes, the shape of the pronotum (especially whether straight-edged or emarginate posteriorly), the chaetotaxy of the mesonotum and the propodeon, give generally the most reliable clues, while specific characters appear to lie in colour, proportions and chaetotaxy of the wings. How far the ring joint can or should be used is doubtful. When consisting of a number of equal rings it may be of some assistance, but in other cases, the basal ring is much the greatest, and it is almost impossible to say whether the succeeding lamina is distinct or not. Even with an oil immersion difficulty may be felt, and there is the further question of the morphological equivalence of these laminae. In the present paper four species assigned to Tetrastichus are described; of these, three are grouped together, mainly on account of antennal and propodeal characters, the fourth I have placed with some others described from dipterous hosts, but if the absence of whorls of hair from the male funicle proves to be more fundamental than the antennal coloration and the propodeal sculpture, possibly all four should go together. In describing the antennae, details are given of the sensoria, which, though rather variable in number on any individual joint, are more constant for the funicle and club as a whole.