408 



— Abdominal segments 2-6 with two narrow bands of conspicuous 



black setulffi which are not distinctly separated from the other dis- 

 cal setulae, the anterior band consisting of only 2 or 3 rows of 

 setulae ; median area of segments covered with short setulae except 

 on several small round patches; each segment with about 10 



rather noticeable long hairs near margins 



Cliironomus nigriccnis (p. 434) . 



20. Ai)ical abdominal appendages with long, regular fringe ; dorsal ab- 



dominal segments usually with conspicuous spotlike groups of 

 setulffi on disc (Tamjtarsus) 21 



— Apical abdominal appendages with either a few very long and con- 



spicuous hairs or bare; or abdominal segments without spotlike 

 groups of setulae 26 



21. Lateral margin of eighth abdominal segment with a simple apical 



spur Tanyiarsus exiguus (p. 495) . 



— Lateral margin of eighth abdominal segment with several spines at 



apex 22 



22. Fourth dorsal abdominal segment with a single patch of black 



spines near base ; no other strong sette present 23 



— Fourth dorsal abdominal segment with 2 anterior patches and 



other conspicuous setulae 24 



23. Third abdominal segment with patch of black spines near base 



Tanytarsus sp. A (p. 530) . 



— Third abdominal segment without patch of spines near base 



Tanytarsus sp. B (p. 530) . 



24. Fourth abdominal segment with two patches of black spines near 



base and a few scattered seta? on surface 



Tanytarsus dives (p. 488) . 



— Fourth abdominal segment Avith two longitudinal series of black 



setffi extending caudad of the patch near base 25 



25. Third abdominal segment with two transverse patches of black 



spines near posterior margin, which are almost connected at mid- 

 dle of segment Tanytarsus dissimilis. 



— Third abdominal segments with two isolated, rounded patches of 



black spines near posterior margin 



Tanytarsus dissimilis "var. r/" (Johannsen). 



26. Thoracic respiratory organs indistinguishable 27 



— Thoracic respiratory organs distinct 29 



27. Abdominal dorsal segments 2-8 with posterior margins armed with 



a transverse series of closely placed teeth, and a large patch of 

 smaller setulae occupying an area from base to beyond middle, 

 extending well towards lateral margins near base and tapering to 

 a point on median line posteriorly Metriocnemiis knahi. 



— Abdominal segments with or without posterior transverse row of 



teeth but without conspicuous dorsal basal patch 28 



