ACARINA ' 449 



(Fig. 704). Body red, 4 mm. long: in 



E. extendens (0. F. Miiller) 

 ponds; cosmopolitan and common 



Subfamily 3. HYDRACHNINAE. 



Body soft, sometimes with chitinous plates; 4 eyes, 2 on each side 

 and sometimes another in the middle ; rostrum usually elongate, forming 

 a snout, at the end of which is the mouth; mandibles 1-jointed, long and 

 needle-like; pedipalps chelate: 2 genera. 



Hydrachna 0. F. Miiller. Body oval or round; legs rather short, 

 the last 3 pairs with swimming hairs; genital pore between the last 2 



Fig. 703 



Fig. 704 



Fig. 705 



Fig. 703 — Limnochares aquatica (Banks). A, ventral aspect; B, dorsal eye plate. 

 Fig. 704 — Eiflais extendens (Wolcott). A, ventral aspect; B, dorsal eye plate. Fig. 

 705 — Hydrachna yeoyraphica i. Wolcott). 1, coxal plates; 2, genital plate. 



pairs of legs; the larvae attach themselves to aquatic insects: about 33 

 species, 8 American. 



H. geographica (Mlill.) (Fig. 705). Body oval, arched, dark red in 

 color with dark spots on the back; length 7 mm.: often common; 

 cosmopolitan. 



Subfamily 4. HYDRYPHANTINAE. 



Body soft, sometimes with chitinous plates, and red or brownish in 

 color; 1 or 2 eyes on each side and sometimes a median eye; coxal plates 

 in 4 groups : the larva leaves the water and is parasitic on aerial insects, 

 returning to the water to complete its transf oimation ; 13 genera. 



Key to the genera of Hydryphantinae here described : 



Oi One eye on each side contained in a chitinous capsule, and a median eye. 



&i Swimming hairs on legs 1. HYDRYniANTES 



62 No swimming hairs 2. Thyas 



O2 Two eyes on each side and no median eye 3. Diplodontus 



1. Hydryphantes Koch. Swimming hairs on the last 3 pairs of 

 legs ; median eye surrounded by a chitinous plate, but no other chitinous 

 plates on the dorsal surface : 17 species. 



H. ruber (DeGeer) (Fig. 706). Body 2 mm. long, red in color, often 

 tending to be dark: in wood ponds, especially in the springtime. 



