108 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



Chetimatopsyche Wallengren 



Cheumatopsyche Wallengren (1891, p. 142). 

 Genotype, monobasic: Hydropsyche lepida 

 Pictet. 



Of the 18 species of this genus described 

 from North America, we have taken 9 in 

 Illinois. The remaining species are distrib- 

 uted in diverse parts of the continent. In 

 Illinois, different members of the genus fre- 

 quent almost every type of stream in the 

 state. Not only do they occur in streams 

 ranging from small brooks to the largest 

 rivers but can frequently succeed to some 

 extent in streams too polluted for almost 

 any other caddis flies. 



The female genitalia have definite con- 

 cavities or invaginations in the sides of the 

 ninth tergite. These seem to be correlated 

 very closely in each species with the shape 

 of the apical segment of the male claspers, 

 and give definite indication of a "lock and 

 key" relationship. 



To date no structural characters have 

 been found to identify the larvae to species. 

 All five of the reared Illinois species have 

 the larval frons notched in the middle, fig. 

 414, no conspicuous head or pronotal pat- 

 tern, and a general habitus similar to that 

 of Hydropsyche; minuscula differs in lack- 

 ing the notch in the frons. 



KEY TO SPECIES 

 Adults 



1. Apex of abdomen with a pair of long 



claspers, fig. 397 (males) 2 



Apex of abdomen with no long append- 

 ages, fig. 391 (females) 11 



2. Apical segment of claspers short, not 



produced into a tapered point, fig. 



394 3 



Apical segment of claspers long, pro- 

 duced into a tapered point, figs. 396, 

 398 4 



3. Apex of tenth tergite bearing a pair of 



pointed, dorsal lobes which are held 



close together, fig. 395 



minuscula, p. 1 10 



Apex of tenth tergite bearing a pair 

 of wide, lateral lobes which are not 

 approximate on meson, fig. 394. . . . 

 sordida, p. 1 10 



4. Apical segment of claspers half length 



of basal segment, fig. 396 .... oxa, p. 1 10 

 Apical segment of claspers shorter, 

 only one-fourth to one-fifth length 

 of basal segment, fig. 397 5 



5. Lobes of tenth tergite reflexed and up- 



turned to form a sharp, pointed, 

 apical ridge and just basad of it a 

 digitate, setose lobe as in fig. 397. . . 



speciosa, p. 1 14 



Lobes of tenth tergite not reflexed to 

 form such distinct and apparently 

 separated parts 6 



6. Apical segment of claspers with a 



broad, triangular base and a short, 

 tapered apex, fig. 398. . . .burksi, p. 113 

 Apical segment of claspers longer, with 

 base not nearly so wide in relation to 

 apex, fig. 400 7 



7. Apical lobes of tenth tergite sharply 



angled, apex bent back and bearing 

 an apical, thick cluster of stout, 

 curved setae as in fig. 399. . .lasia, p. 114 

 Apical lobes of tenth tergite not 

 sharply angled 8 



8. Apical lobes of tenth tergite short, 



more or less circular and at right 

 angles to linear body axis, fig. 400. . 



analis, p.l 12 



Apical lobes at apex of tenth tergite 

 either longer, fig. 402, or not at all 

 circular, fig. 401 9 



9. Apical lobes of tenth tergite appressed 



to tergite, appearing rounded at 

 apex from both lateral and caudal 

 view, and set diagonally to linear 



body axis, fig. 401 aphanta, p. Ill 



Apical lobes of tenth tergite not ap- 

 pearing rounded at apex from lateral 

 and caudal view, and not set diag- 

 onally to linear axis, fig. 402 10 



10. Apical lobes of tenth tergite perpen- 



dicular, rounded at apex and shorter, 



fig. 402 campyla, p. 113 



Apical lobes of tenth tergite angled 

 caudad, pointed at apex and longer, 

 fig. 403 pasella, p. 113 



11. Ninth tergite without pouchlike lateral 



invaginations or pockets, figs. 404, 



405 12 



Ninth tergite with pouchlike lateral 

 invaginations or pockets, figs. 406- 

 413 13 



12. Dorsal portion of ninth tergite wide; 



lateral portion with a small pit and 

 a slightly raised line running ventrad 



from it, fig. 404 minuscula, p. 110 



Dorsal portion of ninth tergite very 

 narrow; lateral portion with a large 

 concave area bounded toward an- 

 terior margin by a sinuate ridge and 

 cutting beneath dorsal portion, fig. 

 405 sordida, p. 110 



13. Lateral invagination short and small 



and situated far from postero-ven- 



tral point of segment, fig. 406 



burksi, p. 1 13 



