THE WATER-MITES (HYDRACARINA) 



863 



18 (7) Distal extremity of pal. seg. 4 slightly or not at all produced be- 



yond the insertion of seg. 5, but the latter free, tapering, the 



tip bearing smaU claws or teeth, or ending in a sharp point. 



Family Hygrobatidae . . 19 



19 (22) Pal. seg. s sharply pointed, claw-like, opposable to the projecting 



distal flexor margin of seg. 4, forming a sort of pincer. 

 Body entirely covered by a porous sheet of chitin, divided by 

 a suture into a smaller dorsal portion and a larger ventral. 

 Legs with swimming hairs. Subfamily Arrhenurinae. . 20 



20 (21) Genital area lying between epp. IV, the cleft flanked by large valves 



each bearing 3 or 4 acetabula. 



Krendowskija Piersig 1895. 



A dark brown mite of medium size, broadly 

 oval in form; witli the capitulum movable and 

 protrusible, and the camerostom developed into 

 a long rostrum, sabre-like and curved upward. 

 One American species, K. ovaia Wolcott, occur- 

 ring rarely in Wisconsin and Michigan. Other 

 species are described from Venezuela and southern 

 Russia. Each is a little over i mm. in length. 



Fig. 1330. Krendowskija ovata Wolcott. Epimeral 

 area and genital area, female. X 75. Inner side, left 

 palpus, female. X 250. Side view of female, showing 

 proboscis. X 60. (After Wolcott.) 



21 (20) Genital area lying posterior to epp. IV, the cleft flanked by two 

 plates forming together an elliptical or circular area, beyond 

 which are laterally extended, wing-like plates with numer- 

 ous acetabula Arrkenurus Duges 1834. 



li^ 



A B CD 



Fig. 1331. Arrkenurus. A, A. forpicatus Neuman; dorsal surface of female. X 27. B, Palpus of 

 A. albator (Miiller), outer side, male. X 113- C, A. maculator (Miiller), dorsal surface, male. X 30. 

 Z), .4. g/o6fl/or (MuUer), dorsal surface, male. X39. All European species. (Modified from Piersig.) 



The females of this genus are approximately oval in form and possess few characters by 

 which they may be distinguished, but the males are highly and variously modified in form and 

 possess complicated accessory sexual structures, including a copulatory organ, the petiole. Leg 



