Hydrachnellae 267 



dofeltria) ; palpal segment iv with many teeth or hair tubercles on 

 inner margin 24 



Epimera i usually united with one another and without median 

 suture; posterior margin of rostrum frequently united with epi- 

 mera i; legs without swimming hairs; genital organ usually with six 

 suckers, in rare cases more, but not over twenty suckers on each 

 side; genital suckers distinctly disklike; palpal segment ii with peg 

 or sclerotic tooth on inner side; palpal segment iv without inner 

 tooth but perhaps with small tubercle bearing setae Hygrobatidae 



24. Without narrow rostrum, at best with short mouth cone 25 



With narrow rostrum about one-third length of organ; genital 

 plates possess many small, porelike suckers; legs with swimming 

 hairs Nautarachnidae 



25. Usually found in stagnant waters and also in slow-moving water 

 but seldom in cold streams; body usually weak-skinned, smooth, 

 and seldom more or less entirely armored; palpal segment iv with 

 conelike protuberance on inner margin; genital suckers usually 

 disklike and distinct, seldom small and porelike; legs usually with 

 swimming hairs; leg in of male without processes 26 



Small mites usually living in streams; with flat body, dorsum with 

 more or less extensive plate which covers anterior and median 

 dorsal region and which is surrounded by small, paired plates in 

 striated region; palpal segment iv without conelike projection on 

 inner margin; epimera iv with large, linear expansion on lateral 

 margin; legs without swimming hairs; leg in of male usually with 

 processes; genital organ of male has many small, porelike suckers 

 on large, medianly united plate and has small genital opening; 

 genital opening of female large, lying between two genital plates 

 and often cleftlike, extending around terminal part of body 



Feltriidae 



26. Body without plates; distal palpal segment with stout spines, some 

 hooklike, for grasping gills of crab- on which it is parasitic; no 

 swimming hairs on legs; large gland on coxa iv; coxae arranged 

 in two groups, lateral groups contiguous; four pairs of genital 

 suckers on plates; genital opening on rear, far from epimeral re- 

 gion; no eyes in female; pair of eyes in immature male 



Astacocrotonidae 



Gland pores of skin often conelike, raised; basal segments of 

 chelicerae usually united medianly with one another; palpal seg- 

 ment III often with very long, lateral spine; posterior part of epi- 



