868 FRESH-WATER BIOLOGY 



42 (43) Body laterally compressed, epimeral plate extending up on the lat- 

 eral surface, leaving only a dorsal median furrow. 



Frontipoda Koenike 1891. 



A mite of medium size, somewhat less than 

 I mm. long, looking curiously like a very flat 

 elliptical seed, emarginate at the hilum where 

 the legs are bunched together; usually of a 

 greenish color. One species, frequent in our 

 northern lakes and apparently identical with the 

 one generally distributed European species, F. 

 musculus (Mijller). 



Fig. 1341. Frontipoda musculus fMiiller). Ventral 

 surface, female. X31. Outer side of palpus, female. 

 X 93. (Modified from Piersig.) 



43 (42) Body not so decidedly compressed, epimeral plate not extending 

 upward on the lateral surface. . . . Oxus Kramer 1877. 



A form of medimn size, different species vary- 

 ing in length from 0.64 to 1.4 mm., with body 

 elongate in form; legs crowded toward the an- 

 terior end. Known in North America only from 

 Wisconsin, where the one species seems to be 

 rare. This is undescribed, but is similar to 0. 

 ovalis (Miiller) and O. slrigalus (Miiller) the 

 common European forms. 



Fig. 1342. Oxus ovalis fMiiller). Ventral surface, 

 female. X 30. Oxus slrigatus (MuWer). Outerside, 

 palpus female. X 90. (Modified from Piersig.) 



44 (23) Epimera arranged in groups, in the female always clearly separate 

 from one another, in the male closer together but distinct, 

 only in rare cases in contact or tending in a slight degree to 

 fuse 45 



45 (64) Epimera in four groups, in the male in some cases only a narrow 

 interval between them 46 



