also on the dorsum of segment 7; segment 9 with a median tracheal gill. 

 Anal legs conical and broad; claws short. Case sac -shaped, broad, dorso- 

 ventrally compressed, with a round anterior opening and a slitlike posterior 

 opening. 



Young larva. Head broader than long; body tapering posteriorly. 

 Difference in length of legs smaller than in the full-grown larva. Dorsum 

 of abdominal segments 1—8 with transverse tergites; dorsal and ventral 

 processes of abdomen absent; segment 9 completely sclerotized, with a 

 median tracheal gill. Anal legs long; their claws are thin, without tracheal 

 gills. 



Pupa. Antennae short, reaching abdominal segments 2—4. Labrum with 

 one pair of setae near the anterior margin and two pairs of setae near the 

 posterior margin. Natatorial setae present on segments 1 and 2 of the mid- 

 tarsi. Presegmental plates elliptical; postsegmental plates rounded. 



Mode of life and habitats. Plant thickets in water bodies with 

 a slow current. 



Distribution. Northwest, west and central belt of the European 

 USSR. In addition, Europe, North America, recorded in India. 



3 60 1. Ithytrichia lamellaris Eaton 



Morton, 1888a:171-173. - Klapalek, 1897:6-9.- Richters, 1902:19-21.- 

 Ulmer, 1902a:360-366; 1903:134; 1909:134, 223, 293, Figure 349. - Lundblad, 

 1918,39:342-343.- Lauterborn and Rimsky-Korsakow, 1903:280-288, 

 Figures 1-6.- Siltala, 1904b:20-22. - Lestage, 1921 :450-452, 

 Figures 144-145. - Lepneva, 1940:202. - Nielsen, 1948:114-132, 139-140, 

 Figures 3, E, 4, E, 6, E, K, 7, H, I, K, L, 43-50, 52, D, Plate II, Figures 6-22, 

 Plate III, Figure 2 7, 28. 



Full-grown larva. Length at beginning of 5th stage 1.05 mm, at end of 

 5th stage 0.3 mm; ratio of length of head, thorax and abdomen at beginning 

 of stage 10:35.5:12.5, at end of stage 10:14.5:82. A remarkable character 

 is the presence of sucker- shaped, dorsal and ventral appendages on the 

 abdominal segments (Figure 477). 



Head (Figure 4 78) broad in the middle, slightly dorsoventrally compressed 

 (ratio of height to width 0.72), narrower anteriorly; frontoclypeus large, 

 broad; coronal suture of head even shorter than in Orthotrichia; gula 

 fused with pregula, its posterior angle blunt. Eyes situated at about mid- 

 length of head; sensillae of antennae long, directed forward (Figure 479); 

 a seta at the base of the sensilla. Setae on head light; the 3 anterior - 

 margin setae situated in the angles of the sclerite; intermediate anterior - 

 margin seta and anterior and posterior frontal setae curved, recumbent 

 toward the middle, like seta 16 and the small seta 13; seta 9 much longer 

 than the others; near it the thin short seta 11; seta 10 curved anteriorly, 

 thick, relatively long; setae 7 and 8 straight and short; setae 12, 14 and 15 

 thin, about the same length; setae 17 slightly shorter; seta 18 spinelike. 



Labrum (Figure 480) narrower anteriorly; membranous anterior margin 

 of labrum rounded laterally, straight in the middle, without median notch; 

 anterior angles not marked; median notch of dorsal sclerite shallow; 

 a horseshoe-shaped thickening near the anterior margin of the sclerite; 

 posterior-angle sclerites long, slightly curved, slightly asymmetrical. 



400 



