266 Acarology 



19. Genital suckers present; fresh-water mites 20 



Genital suckers not present: marine mites, on littoral of seas 



Pontarachnidae 



20. No shears formed by palpal segments iv and v 21 



Clawlike palpal segment v so hinged to dorsal distal portion of 

 segment iv that two segments form pincers; two fine sensory or 

 grasping setae on inner margin of segment v; segment v usually 

 with strong spine; body armored 30 



21. Lateral eyes united (Astacocrotonidae with pair of eyes); leg iv 



as a rule with claws 22 



Lateral eyes separated from each other; leg iv usually without 

 claw; palpal segment ii often with sclerotic cone on inner edge; 

 with three pairs of genital suckers Limnesiidae 



As above but with many genital suckers Neotorrenticolidae 



22. Body as a rule membranous; seldom with more or less extensive 

 dorsal plates; very seldom with completely hardened ventral and 

 dorsal shields; epimera usually in four groups; sutures between 

 them usually present but in several cases median suture between 

 first epimera disappears or suture between third and fourth pair 

 of plates not fully developed; genital organ of cutaneous or mem- 

 branous form with distinct plates containing the more or less disk- 

 like, seldom porelike, suckers; palpal segments ii, in, and iv fre- 

 quently with cones or tubercles on inner margin 23 



Body almost entirely armored, dorsal and ventral armor generally 

 separated by narrow dorsal suture; in a few cases genital organ 

 in membranous area, or only ventral armor present; body usually 

 flat, often discoidal; epimeral sutures lacking; genital organ be- 

 tween epimeral region and posterior end of body; the six, eight 

 or more genital suckers lie upon more or less distinct plates, and 

 ledgelike or roundish plates often united with ventral shield; if 

 genital organ lies in vicinity of epimeral region then orifice usually 

 in opening of ventral shield, and genital suckers lie on valvelike 

 plates, or under or at inner edge of flaplike genital "rolls" which 

 unite with ventral shield; the medial distal edge of palpal seg- 

 ment IV without sclerotic projection 27 



23. Epimera i separated from one another behind rostral base by su- 

 ture or skin area; rostrum, as a rule, lies free and is not united with 

 epimeral region; legs generally have swimming hairs; palpal seg- 

 ment II without pegs or cones on inner margin (exception: Pseu- 



