AQUATIC INSECTS 945 



30 (27) Last segment usually with hooks, no spiracles apparent. Larva 



transparent Corethra. 



31 (12) Body cylindric, or depressed fusiform 32 



3 2 (33, 34) Body ending in two fleshy points Family RHYPHIDAE. 



33 (3 2 > 34) Body ending in a tapering segment tipped with a tuft or circlet 



of hairs Ceratopogoniae of CHIRONOMIDAE. 



34 (32, 33) Body ending in a strongly chitinized terminal segment, usually 



produced in chitinous respiratory tube. . . PSYCHODIDAE. 



35 (7) Prothorax with one or two prolegs 36 



36 (57) A pair of prolegs beneath the prothorax, and another pair at the end 



of the abdomen Family CHIRONOMIDAE . . 37 



37 (38) Abdomen with prominent rounded elevations or cushions, with rows 



of teeth on the inferio-anterior angles of the segments. 



Psamathiomyia . 



38 (37) Abdominal segments without cushions 39 



39 (40) With retractile antennae, the latter often quite long, long stiltlike 



legsj the caudal tufts of hair mounted on cylindrical processes. 



Tanypus. 



40 (39) Not with all the above characters 41 



41 (44) With the two caudal hair tufts mounted on cylindrical projections. 42 



42 (43) With blood gills on venter of eleventh segment. . . Hydrobaenus. 



43 (42) With blood gills only at end of twelfth segment. . . Metriocnemus. 



44 (41) Caudal tufts on small rounded papillae 45 



45 (48) Antennae elongate, at least one-half as long as and often as long as 



or longer than the head 46 



46 (47) Antenna with one or two sense organs at tip of second segment. 



(Rendered visible in preserved material by soaking in 

 water) Tanytarsus. 



47 (46) Antenna at most with a seta at tip of second segment at side of the 



third segment Corynoneura. 



48 (45) Antennae short ....... 49 



49 (50) Larvae usually blood red; eleventh body segment with two pairs of 



blood gills Chironomus (in part) . 



50 (49) Larvae greenish, yellowish, or whitish 51 



51 (52) The maxilliary palpus usually noticeably longer than broad. Larva 



in pools, pond water, or slow streams .... Chironomus. 



52 (51) Palpus about as long as broad 53 



53 (54) Full-grown larva not over 6 mm. long, green or bluish-green in color. 



Anterior abdominal segments of greater diameter than the 

 posterior ones. Mandibles often transversely wrinkled; 

 the anterior prolegs usually with pectinate setae. 



Cricotopus, Orthocladius. 



54 (53) Full-grown larva over 6 mm. in length; mandible not transversely 



wrinkled 55 



55 (56) Labium with teeth all rounded Diamesa. 



56 (55) Labium with middle tooth broadly truncate Thalassomyia. 



