874 FRESH-WATER BIOLOGY 



65 (66) Leg segs. I 5 and I 6 modified Atractides Koch 1837. 



Small to medium-sized mites, vary- 

 ing in length from 0.48 to 1.5 mm. 

 with surface soft and striate, or with 

 a flexible or hard porous covering; 

 swimming-hairs present. Species 

 few in this country, rare, in northern 

 lakes. 



Fig . 1 3 5 2 . A trac tides s pint pes Koch , a 

 species common to Europe and America. 

 Ventral surface, female. X 25. Outer 

 side of left palpus, female. X 103. 

 (Modified from Piersig.) 



66 (65) Leg segs. I 5 and I 6 normal Hygrobaies Koch 1837. 



*^ 



Mites var>'ing in size from small 

 to even large, or 0.5 to 2.5 m_m., 

 brightly colored in many cases, with- 

 out swimming-hairs, but active, and 

 certain species frequently, if not regu- 

 larly, pelagic. Several species of gen- 

 eral distribution in northern United 

 States and Canada. 



Fig. 1353. Hygrobaies longipalpis 

 (Hermann), a species found in North 

 America, Europe and Western Asia. 

 Ventral surface, female. X 13 • Outer 

 side, palpus, female. X 125. (Modified 

 from Piersig.) 



In collecting water-mites with the Birge net one will ahnost always findin 

 the collection specimens of another mite of small size, brown in color, with 

 short legs, with the body indistinctly separated into cephalothorax and ab- 

 domen and with a horny body-covering. This belongs to the horny mites or 

 Oribatidae, probably to the genus Notaspis, and is a vegetable feeder living on 

 aquatic plants beneath the surface of the water. It can not swim, and will 

 either cling to objects at the bottom of the dish or float on the surface.^ Sev- 

 eral species occur and are generally distributed. The species increase in size 

 and num.ber to the southward. 



