404 



— Labial teeth not acutely pointed 23 



23. Central tooth simple, regularly rounded 24 



— Central tooth with a distinct shoulder (PL XXIX, Fig. 19) 



Tanytarsus exiguus (p. 495) . 



24. Sides of labium diverging slightly, the outline of labium almost 



subtriangular 25 



— Sides of labium diverging widelv, anterior outline slightly con- 



vex .26 



25. First lateral tooth simple, regularly rounded Cricotopus exilis. 



— First lateral tooth fused with second so that latter appears to be a 



mere shoulder to the first Ortlwcladius fugax. 



26. Antennse remarkably elongated, their entire length rather more 



than equal to that of head Tanytarsus dives (p. 488). 



— AntennjE not exceptionally long, shorter than head 



Tanytarsus sp. C (p. 531) . 



27. First lateral tooth distinctly shorter than second lateral and cen- 



tral teeth Cliironomus dorsalis. 



— First lateral tooth not shorter than second 28 



28. Second antennal joint with 2 slender processes, which have their 



apices slightly enlarged, in addition to the normal continuation of 

 the antenna Tanytarsus exiguus (p. 495) . 



— Second antennal joint with only one auxiliary process, which is 



sharp apically Tanytarsus dissimilis. 



29. The bifid central tooth very short, flanked by a very broad portion 



which occupies about half the remaining area of labium, and is 

 succeeded laterally by 4 or 5 short teeth; mandible very acutely 

 pointed ; apical jointed portion of antenna about a fourth as long 

 as basal joint OrtJiocladius flavus. 



— The bifid central tooth long and distinct, no large untoothed area 



on each side 30 



30. Central tooth shorter than second (PL XXIX, Fig. 6) . . 



Chironomus fulviventris. 



— Central tooth not distinctly shorter than second 31 



31. The central 4 teeth of about equal size, the next one on each side 



distinctly longer and very distinctly darker, the 6 together form- 

 ing a slightly concave anterior line, sides but slightly divergent 

 posteriorly; basal hair remarkably long (PL XXIX, Fig. 23) ; 

 antenna as in Figure 11, Plate XXX. .Genus incertus B (p. 533). 



— Labium not as above 32 



32. First lateral tooth very distinctly shorter than the central bifid 



tooth and second lateral, or sometimes closely fused with the 

 former 33 



— First lateral tooth not very short, generally distinctly longer than 



second, the central tooth with a distinct shoulder in Ortlwcladius 

 nivoriundus 34 



