ACAE1NA 



449 



E. extendens (0. F. Miiller) (Fig. 704). Body red, 4 mm. long: in 

 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 O. 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 EylaAs extendens (Wolcott). A, ventral aspect; B, dorsal eye plate. Fig. 

 705 Hydrachna geographica (Wolcott). 1, coxal plates; 2, genital plate. 



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

 species, 8 American. 



H. geographica (Mull.) (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 transformation; 13 genera. 



Key to the genera of Hydryphantinae here described : 



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



61 Swimming hairs on legs 1. HYDBYPHANTES 



6 2 No swimming hairs 2. THYAS 



Oj Two eyes on each side and no median eye 3. DIPLODONTUS 



1. HYDEYPHANTES 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. 



