THE ACAKIXA OR MITES. 



51 



In Aturus the epimeral plate covers nearly the entire ventral surface; one species 

 is known from a small river in Canada. Of Xystonotus and Mideopsis but one species 

 is known in each. The latter is also a common European water mite. 



Fig. 81.— Larva of an Hydrachna attached 

 to leg of an insect; njTnph inside. (Au- 

 thor's illustration.) 



Fig. 82.— Limnesia sp.: Palpus 

 and coxal plates. (Author's 

 illustration.) 



The species of Sperchon (figs. 90, 91) are often found in cold and rapid mountain 

 streams. Three species are known from Canada. They have the palpi enlarged at 



Fig. S^.— Tyrrdlia circularis. 

 (Author's illustration.) 



Fig. 84.— TTiyas sp. (Original.) 



base, and the second joint bears a strong spur below. The sucking disks each side of 

 the genital opening are nearly concealed by lateral flaps. The legs have no special 

 swimming hairs, and coxae III and IV are widelv separated from I and II. 



Fig. 85.- 



-Mandible of Thyas sp. 

 (Original.) 



•Palpus of Thyas 

 (Original.) 



Limnesia (fig. 82) is a large genus. Three species have been recorded from Canada, 

 two of them European. They have a soft body; the hind legs are well provided ^vith 

 swimming hairs, and the fourth tarsus lacks the claws, but is pro\dded with a bristle 



