Aphiochaeta. 203 



in the middle of the front margin so that an unchitinized part is seen 

 here, and I think this may be in connection with some special organ 

 present in this place; this feature is sometimes rather conspicuous 

 f. inst. in pijgmaea^ but is also seen in the other species, when the seg- 

 ments are fully stretched out. In some few species {ruficornis, pygmaea 

 and to a less degree errata and tarsalis) the abdominal tergites in the 

 female are on some segments narrowed in a curious way, and in other 

 species (ciliata, coaequalis) the fourth or [tergata^ breviterga) the third 

 tergite is abbreviated, or the fourth tergite is not at all developed 

 {zonata). Abdomen is sparingly haired with very short hairs, generally 

 only quite slightly longer at the hind margins of the segments; these 

 hindmarginal hairs as a rule increase a little in length backwards, 

 but they may be more or less elongated or sometimes developed as 

 bristles at the hind margin of the sixth segment in the male; in some 

 species the hairs at the sides of second abdominal segment are devel- 

 oped as more or less strong bristles; two species (rufipes and hirti- 

 ventris) have in the male abdomen clothed with curious, long hairs. 

 Legs sometimes with the front tarsi thickened, either the whole tarsus 

 or only metatarsus, and generally the thickening is most pronounced 

 in the male. In single cases the hind tibiæ and metatarsi may be 

 thickened. Hind femora more or less broad. The legs have no single 

 special bristles; the posterior tibiæ have an apical spur; the hind 

 tibiæ have a dorsal hair-seam consisting of dense, palisade-like arranged 

 hairs and generally standing on a slight longitudinal keel; the hair- 

 seam may be straight or more or less deflected; on the posterior side 

 of the hair-seam there is a row of bristles which may vary from 

 rather strong to quite delicate, but always distinctly discernible from 

 the other hairs present; the various development of these bristles 

 form a very important specific character; on the middle tibiæ a similar 

 arrangement is present, only the hair-seam stops here a little before 

 the apex and the bristles are smaller; in a few species there is on the 

 posterior tibiæ a row of bristles also on the anterior side of the hair- 

 seam, but these bristles are smaller than the posterior and generally 

 not going to the apex, or only developed above and few in number. 

 Only two species {nudipes and retroversa^ non-Danish) show simple 

 posterior tibiæ without hair-seam or bristles, and these two species 

 are thus rather aberrant. The legs are for the rest clothed with short 

 hairs; on the anterodorsal side of middle tibiæ towards the end the 

 hairs are a little longer, but not, or not distinctly arranged in rows; 

 on the posterior side of hind tibiæ at apex the short hairs are arranged 



