452 AEACHN1DA 



L. histrionica (Hermann) (Fig. 710). Length of female 2 mm.; 

 breadth 1.7 mm. ; male half as large ; color variable but usually yellowish 

 with dark patches and red spots on the back; legs bright green; eyes 

 red ; body marked with faint wavy lines ; pedipalps very long and thick : 

 very common over the whole country; Europe. 



5. KOENIKEA* Wolcott. Body round, flat or concave on dorsal sur- 

 face, with a long curved rostrum in the female; coxal plates of male 

 fused into a single plate, and in the female into 2 plates; legs with 



Fig. 710 Fig. 711 



710 Limnesia histrionica (Wolcott). Fig. 711 Arrhenurus america 

 shall) . A, ventral aspect of male ; B, ventral aspect of female. 



swimming hairs; numerous minute suckers on each side of the genital 

 pore: 1 species. 



K. concava Wolcott. Body .67 mm. long; eyes 2, widely sepa- 

 rated: common and widely distributed over the eastern and central 

 states. 



6. ARRHENURirsf Duges. Integument very hard and porous; back 

 with a circular furrow enclosing the dorsal shield ; female oval in shape ; 

 male with the hinder end very much prolonged, forming an appendix 4 , 

 eyes widely separated ; coxal plates of the first 2 pairs of legs contiguous ; 

 also those of the last 2 pairs; pedipalps chelate: 150 species, 50 

 American. 



A. marshalli Piersig. Body of male 1 mm. long with the appendix 

 very long, cylindrical and constricted at the base; female .8 mm. long 

 and oval; color blue-green, occasionally orange: cosmopolitan and com- 

 mon, usually the most abundant of the genus. 



A. americanus Ruth Marshall (Fig. 711). Male .92 mm. long; 

 appendix widest at hinder end; color greenish, tinged with red; female 

 1.12 mm. long and ovate in form : abundant in the Middle West. 



* See "New Genera and Species of North American Hydrachnldae," by R. H. 

 Wolcott, Trans. Am. Mic. Soc., Vol. 21, p. 189, 1900. 



t See "The Arrhenuri of the United States," by Ruth Marshall, Trans. Am. Mic. 

 Soc., Vol. 22, p. 85, 1908. 



