86o 



FRESH-WATER BIOLOGY 



5 (2) Pal. seg. 5 free, eye-plate broad, consisting of two lateral portions 



connected by a transverse middle piece. Family EYLAIDAE. 



One genus only Eylais Latreille 1796. 



A red mite with body circular in outline 

 and usually smooth; with palpi slender in 

 form and richly supplied with hairs and 

 spines, many of them feathered; hind legs 

 without swimming-hairs and allowed to 

 trail motionless behind in swimming. 

 Several species, very closely allied and gen- 

 erally distributed and often very abundant. 

 Varying in size from about 2 to 5 mm. 



FIG. 1323* Eylais extendens (M tiller), a Euro- 

 pean species. Ventral surface of female. X 7- 

 Inner side of right palpus. X 69. Eye-plate. 

 X 59- (Modified from Piersig.) 



6 (i) Lateral eyes of the two sides widely separated and in no case borne 



on a common eye-plate 7 



7 (18) Distal extremity of pal. seg. 4 produced beyond the point of inser- 



tion of seg. 5, the two segments together resembling a 

 pair of shears 8 



8 (9) Mandible one-segmented, the terminal portion straight and stiletto- 



like Family HYDRACHNIDAE. 



One genus only Hydrachna Latreille 1796. 



Mites of some shade of red or 

 brown, and sometimes spotted 

 with black, with the body glob- 

 ular, soft, and usually papillated; 

 capitulum produced into a snout. 

 Species numerous, occurring in 

 swamps, lakes and ponds every- 

 where and usually common. 

 Varying from i to even 8 mm. 

 in length. 



FIG. 1324. Hydrachna, geographica 

 (Muller), a European species, also 

 found in New England. The largest 

 described hydrachnid. Ventral sur- 

 face, female. X 4- Palpus. X 16. 

 (Modified from Piersig.) 



9 (8) Mandible two-segmented, the terminal segment curved and claw- 

 like Family HYDRYPHANTIDAE. . . 10 



