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. 13 50. Tiphys liliaceus (M tiller) , the most common 

 European species. Ventral surf ace, female. X 28. Outer 

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



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. 



Fiona 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 constricta (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 



