533 



but occasionally the central tooth is shorter than in the figure, while 

 the first laterals are longer and the outer short teeth are less conspicu- 

 ous. The figure represents the labial plate as flattened by pressure, so 

 that the lateral margins are more divergent than in nature. Anal 

 pseudopods and blood-gills normal in form; anal tufts short, the basal 

 papillae inconspicuous. 



Illinois localities : Illinois River at Hardin and Grafton, by dredg- 

 ing. 



Genus incertus B 



Several larval specimens in the collection of the State Laboratory 

 resemble Cricotopus trifasciatus in having distinct hairs on the tho- 

 racic and abdominal segments, but without rearing the species I have 

 no means of deciding whether it really belongs to Cricotopus. 



Larva. — Length, 3.5-4 mm. Green. Head distinctly longer than 

 broad ; antennae short, about ecjual in length to mandible ( PI. XXX, 

 Fig. 11); labial plate with a very long hair on each side at base 

 (PI. XXIX, Fig. 23) ; anal segments as in Figure 7, Plate XXX; 

 (I can discern but one pair of respiratory organs;) arrangement of 

 hairs on segments as shown in the figure ; claws of posterior pseudo- 

 pods retractile. 



Illinois localities : Illinois River at Grafton and La Grange, and 

 the Sangamon River near its mouth. 



Genus incertus C 



Larva. — Length, 2-3 mm. Green. Head nearly twice as long as 

 broad; eye spots large, confluent; antennae very slender, half as long 

 as head, second joint blackened (PI. XXX, Fig. 8) ; labial plate elon- 

 gate (PI. XXIX, Fig. 22) ; thoracic and abdominal segments without 

 hairs ; anterior and posterior pseudopods elongate, the former with 

 apical claws which are but little weaker than those of the posterior 

 pair ; dorsal blood-gills well developed ; anal tufts weak, basal papillae 

 short and inconspicuous. 



Illinois locality, Illinois River at Dresden Heights, by dredging. 



Very probably this species belongs near Cricotopus, but no attempt 

 was made to rear it. 



Genus incertus D 



Larva. — Length, 5-6 mm. Green. Head about a fourth longer 

 than broad; antennae about a third as long as head (PI. XXX, Fig. 4), 

 consisting of 6 joints; labium as in Figure 18, Plate XXIX, in one 

 specimen with the central division and the one between the central 

 tooth and the first lateral indistinct, as shown by upper outline in the 



