508 



First abdominal segment as in Oe.ochracea with a large, wide, 

 dorsal process and a pale, small, indistinct sclerite near spinulose disk of 

 lateral processes, which are situated more ventral than usual. 



Gills as in Oe. ochracea, presegmental on segments 2—8 in dorsal 

 and ventral rows; segment 2 with one postsegmental pleural gill. 



Tergite of segment 9 (Figure 808) large, whitish yellow; medioanal seta 

 and lateral seta thick, moderately long, situated near posterior margin, 

 pinkish; intermediate seta and anterior-margin seta almost as long as the 

 former, situated some distance from margin; 5—6 similarly large setae, 

 most of them thin, laterally at margin and subapically; primary anterior- 

 angle seta and 2—3 secondary setae thicker than the others. 



Sclerite "b" of anal legs whitish, indistinct; setae large, pinkish; 

 2 thick setae situated above claw longer than the others; a similar thick, 

 but short, pinkish seta dorsally; 2 thin, moderately long, lateral, distal setae. 

 Sclerite "c" brownish, with a small, thin seta. Claw pinkish, with 2—3 dorsal 

 denticles. 



Case straight, with thin walls made of light, loosely cemented sand grains; 

 posterior end slightly narrower (Figure 809). 



Mode of life and habitats. Halophilous. The larvae live in 

 brackish water; coast of Caspian Sea (numerous in some places); Aral' Sea; 

 Lake Chelkar in the Urals; Lake Balkhash, and other brackish and salt 

 water bodies. 



Distribution. Southeastern part of European USSR; Kazakhstan, 

 Western and Eastern Siberia. In addition, Iran, Mongolia. 



3. Oecetis lacustris Pictet 



Klapalek, 1893:107—111, Figure 29.— Struck, 1903:Plate III, Figure 15.— 

 Ulmer, 1903:109, Figure 104.— Siltala, 1905:84—86, 90; 1907:480—482.— 

 Ulmer, 1909:246, 309, Figure 447g.— Lestage, 1921 : 63 9— 647, Figures 221g, 

 k, 222c.— Lepneva, 1940:210.— Hanna, 1958:21— 24. 



Full-grown larva. Length 8— 10 mm; sclerites brighter, ground color 

 yellowish. Head (Figure 810, A) relatively wide; sensilla of antenna small, 

 thin, shorter than anteclypeus; seta small, light. Anterior part of 

 frontoclypeus with 3 pairs of dots, posterior pair with oblong dots closer 

 together; middle and posterior parts of the sclerite with a brownish, 

 median stripe which widens posteriorly and includes 4 large and several 

 small dots. Dorsal stripes distinct, dark brown near anterior branch of 

 frontal sutures; a large, dark dot and 2 large dots along suture further 

 posteriorly; 3 rows of smaller dots lateral to coronal suture; rows of dots 

 on site of lateral stripes; a brownish stripe with small, indistinct, light 

 dots ventrally at occipital foramen; 4—5 large dots lateral to stripe. Setae 

 as in Oe.ochracea. Gula dark, reddish brown, smaller than in 

 Oe.ochracea (Figure 810, B). 



Seta 1 of labrum inform of alight spine. Mandibles as in other species of 

 Oecetis, flat on median side, with 2 large teeth, basal tooth with coarse serra- 

 tion, denticles with blunt, light apex. Maxillolabium as inOe. ochracea. 



634 



