136 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



496 A 



DUALIS 



497 C 



Figs. 494-497. — Oxyet/iira, female genitalia. J, ventral aspect; B, lateral aspect; C, 

 bursa copulatrix. 



Aedeagus with neither neck nor thread, 

 with the tip enlarged and vasiform 

 and containing an eversible group 

 of 5-6 sclerotized spines, fig. 493. . . 

 dualis, p. 139 



10. Eighth sternite truncate, fig. 495, or 



emarginate, fig. 494 11 



Eighth sternite produced into a 

 rounded apex, fig. 497 12 



11. Bursa copulatrix short, with a ventral, 



sclerotized bridge, fig. 494 



pallida, p. 137 



Bursa copulatrix elongate, without a 

 sclerotized ventral bridge, fig. 495. . 

 serrata, p. 136 



12. Bursa copulatrix with a semisclero- 



tized, large, vasiform base, fig. 496 



dualis, p. 139 



Bursa copulatrix with base membra- 

 nous and not vasiform, fig. 497. . . . 

 novasota, p. 138 



Oxyethira serrata Ross 



Oxyethira serrata Ross (1938^, p. 117); cf, 

 9. 



Larva (mature type). — Length 3 mm. 

 Head rounded. Middle and hind legs much 

 more slender than front legs. Abdomen 

 without dorsal sclerites and only slightly 



widened at middle, the segments not set off 

 by constrictions. 



Case. — Fig. 498. Constructed of trans- 

 parent, sheetlike material, without sand 

 grains, narrow at end and tapering evenly 

 to front, end slightly flattened. 



Adults. — Length 2.5-3.0 mm. Color light 

 and mottled. Wings tapered to a slender 

 ape.x ; hind wings slender. Tibial spur count 

 0-3-4. Ocelli present. Male genitalia, fig. 

 485: claspers elongate; tenth segment beak- 

 like ; aedeagus with a short base and elon- 

 gate, cylindrical apex, with a ribbon-like 

 spiral which apparently fuses with the apical 

 portion; eighth segment with a pair of long, 

 lateral processes which are serrate along 

 the dorsal margin. Female genitalia, fig. 

 495 : eighth sternite wide and slightly emar- 

 ginate, ninth segment narrow and sclero- 

 tized, with a pair of long, internal rods; 

 tenth segment nearly ovate; bursa copulatrix 

 composed of three saclike lobes. 



This species is apparently confined in Illi- 

 nois to the glacial lakes in the northeastern 

 corner of the state. The cases have been 

 found in large numbers under stones in 2 

 or 3 feet of water along open beaches. Adult 

 emergence seems confined to the earlier part 



