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FRESH-WATER BIOLOGY 



35 (32) Acetabula arranged along the posterior margin of the body, in one 

 or more rows, running forward on either side nearly to the 

 point of insertion of leg IV, which leg is, in the male, modi- 

 fied Aturus Kramer 1875. 



Very small mites, varying in length from 0.33 to 

 0.38 mm., with the posterior margin of the body 

 deft; no swimming-hairs; leg IV of male with 

 segs. 4 to 6 strikingly modified. One species, 

 Aturus mirabitis, is recorded from Canada by 

 Koenike. The genus is characteristic of rapidly 

 flowing streams. 



Fig. 1337. Aturus sraber (Kramer), a European spe- 

 cies. Ventral surface of male. X 6i. Outer side of 

 palpus, female. X 150. (Modified from Piersig.) 



36 (31) Suture open anteriorly, the two ends passing around on to the ven- 

 tral surface 37 



37 (38) Genital area with 4 acetabula on each side . . Axonopsis Piersig 1893. 



A very small, brightly-colored mite 

 about 0.45 mm. in length, with a median 

 cleft in the posterior margin of the oval 

 body; the anterior epimera extended 

 beyond the capitulum; few swimming- 

 hairs. One North American species, 

 rare, in northern lakes, apparently the 

 same as the European A. complanata 

 (MuUer). 



Fig. 1338. Axonopsis complanata (MuHer). 

 Ventral surface of female. X so. Outer 

 side, right palpus. X 123. (Modified from 

 Piersig.) 



