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FRESH-WATER BIOLOGY 



51 (so) Leg IV ending in a point, a long hair a little back from the tip, swim- 

 ming-hairs present Limnesia Koch 1837. 



A mite varying from small to large in size, 

 or from o-s to 2 mm. in length, with oval 

 body, surface striate, sometimes papillose, 

 and even developing a chitinous meshwork; 

 two eyes on each side separate. Handsome 

 mites with bright red spots, very active, and 

 among the most powerful and voracious of 

 all. Ten North American species; generally 

 distributed and found under very varied con- 

 ditions. 



Fig. 1345. Limnesia histrionica (Hermann), 

 the most widely distributed North American spe- 

 cies, also found throughout Europe. Ventral sur- 

 face, female. X 16. Outer side, palpus, female. 

 X51. (Modified from Piersig.) 



52 (47) Genital acetabula along the margin of the cleft, covered laterally 

 by flaps; without swimming-hairs. Sperchon Kramer 1877. 



Body oval, rarely with small chitinous 

 plates, smooth, or papillate; capitulum very 

 movable. A genus found in northern and 

 mountain lakes and streams. Three species 

 recorded from Canada. Species small to 

 medium in size, in length 0.5 to 1.5 mm. 



Fig. 1346. Sperchon glandulosus Koenike, a 

 species recorded both from Europe and Canada, 

 Ventral surface, female. X 24. Outer side of 

 palpus, female. X 94- (Modified from Piersig.) 



S3 (46) Genital area lying posterior to epp. IV, at most only its anterior 

 end lying between their emarginate posterior angles; an 

 ancoral process present. . . Subfamily Pioninae. . 54 



