Mesonotum, metanotum and abdominal segment 1 are the widest part of 

 the body. Prothorax and mesothorax convex dorsally, especially in 

 nonsclerotized posterior part of mesonotum; the body forms a blunt angle 

 at anterior margin of metathorax, forming a more or less conspicuous hump. 



Legs without the characteristic light chaetoids of Apataniini in distal 

 part of trochanter and at base of femora. Gills usually present only on 

 abdominal segments 2 — 3, only postsegmentally, rarely also on segment 4. 

 Case made of coarse sand grains, with rough surface. 



Mode of life and habitats. Littoral zone of Lake Baikal, on 

 firm bottom, on stones, stony deposits, and on sandy-stony, and sandy bottom; 

 among sparse vegetation, usually at a depth of 2—10 m; often in large 

 numbers on stones. The species of this tribe avoid silt bottom. 

 Phytophagous; young larvae feed on microbenthos, full-grown larvae also 

 eat large filamentous algae and plants with narrow, delicate leaves, such 

 as Myriophyllum (Bebutova, 1 941 : 86-87). 



Distribution. USSR: Lake Baikal. Absent outside USSR. 



Key to Genera* 



(except Radema Hag.) 



1 (4). Horn on prothorax absent. Gills on abdomen present. 



2 (3). Small secondary setae present singly on head. Gula in form of 



nearly equilateral triangle with blunt, dark posterior angle and 

 almost straight sides 1. Thamastes Hag. (p. 105) 



3 (2). Small secondary setae present in large numbers on head. Gula 



slightly oblong, with curved sides, posterior angle lighter than 



other parts of sclerite, sometimes slightly produced and 



pointed 2. Baicalodes Mart. (p. Ill) 



4 (l). Horn on prothorax present. 



5 (6). Gills present 3. Baicalina Mart. (p. 116) 



6 (5). Gills absent or rudimentary, and only on segment 2 



4. Baicalinella Mart. (p. 130) 



1. Genus Thamastes Hagen 



Full-grown larva. Length 9— 13 mm. Head dark chestnut brown; gula 

 in form of a nearly equilateral triangle; secondary setae of head small, 



• Schmid (1953:110) placed the genera Baicalina Mart., Ba icalinella Mart, and Baicalodes Mart. 

 in a single, broadly defined genus, Radema Hagen. This does not take into account the morphological 

 characters of the larvae, however. In fact, the larvae of these genera (Martynov, 1914:51—74; 1924:93—96) 

 differ in a number of important biologic and taxonomic aspects, including the structure of the sclerites and 

 especially the development of the covering sclerites, form of the gula, chaetotaxy of the head, presence 

 or absence of a prothoracic horn, and presence and number of gills. Such characters are used in other 

 groups for the definition of genera and even higher categories, up to subfamily. Moreover, the larvae of 

 .Baicalina Mart, and Baicalinella Mart, placed by Schmid in the genus Radema differ from the 

 larvae of Thamastes much moremarkedly than do the larvae of Baicalodes Mart.; the larvae of 

 the latter 2 genera show a number of close resemblances. Weretain, therefore, the genera Baicalodes Mart., 

 Baicalinella Mart., and Baicalina Mart, in addition to Radema Hag. and Thamastes Hag. 

 The larvae of Radema Hag. (R. infernal e Hag., R. setosum Mart., R. uncinatum Mart.) are 

 unknown. We assume that they are more closely related to Apatania than to the larvae of other 

 Baicalinini. 



105 



