THE WATER-MITES (HYDRACARINA) 



873 



62 (63) Medial margin of ep. IV reduced to merely a medial angle which 

 forms a common angle with the medio-posterior angle of 

 ep. Ill; leg segs. IV 5 and IV 6 of male modified. 



Tiphys Koch 1837. 



Rather small mites, in length from 0.54 to i mm., 

 with swimming-hairs and the hind leg of the male 

 strikingly modified. Few North American species, 

 rare, in our northern lakes, as yet not studied. 



Fig. 1350. Tiphys liUaceus (Miiller), the most common 

 European species. Ventral surface, female. X 28. Outer 

 side, nght palpus, female. X 123. (Modified from 



Piersig.) 



63 (62) Medial margin of ep. IV not reduced, and, owing to the angle on 

 the posterior margin, ep. IV more or less clearly five-sided. 



Piona Koch 1837, 



Oval or elliptical forms of 

 various sizes, from 0.45 to 3 mm. 

 long, often brightly colored, with 

 swimming-hairs, and with char- 

 acteristic modifications of leg 

 segs. Ill 6 and IV 4 in the male, 

 the latter serving to assist in 

 grasping the female in pairing, 

 the former to carry the semen 

 to the female genital opening. 

 Hardy, active mites, adapting 

 themselves to a great variety of 

 conditions. More than twenty 

 American species, generally dis- 

 tributed over the continent. 



Fig. 1351. Fiona rufa (Koch), a 

 European species. Ventral surface, 

 female. X 22. Outer side, palpus, 

 female. X 77- (Modified from 

 Piersig.) Fiona constricla (Wol- 

 cott), an American form. Leg seg- 

 ment IV 4, male. X 107. (After 

 Wolcott.) 



64 (45) Epimera in three groups, epp. I being fused together behind the 



capitulum, the groups also often close together in the male. 



Subfamily Hygrobatinae . . 65 



