THE ACARIXA OR MITES. 



75 



Fig. liS.—Pneumonysus: 

 Beak, claws, and stigmal 

 plate. (Author's illus- 

 tration.) 



' most, if not all, of these myrmecophilous forms are scavengers, and their presence use- 

 ful to the health of the colony. The ants sometimes take care of the mites when the 

 nest is disturbed, and carry them to a place of shelter. One species of Hypoaspis {H. 

 equitans Michael) was frequently observed to jump up on an 

 ant and ride about for a while, the ant taking no notice of its 

 rider. It appears that each species of mite prefers to live 

 with a certain species of ant, but several kinds of mites hive 

 been found in the same nest. The mites disappear when the 

 ants desert the nest. Fully 50 of these m>Tmecophilous mites 

 are known from Europe, a number from Australia, South 

 Africa, and South America, but few from this country. 



The classification of this family adopted by Berlese and 

 some other European acarologists is very unsatisfactory, 

 since most of the divisions are based on characters observ- 

 able in but one sex. A genus should hardly be based on 

 such characters, certainly not a subfamily. His classifica- 

 tion is about as folio .vs: 



1. Male genital opening in front of the sternal plate 2 



Male genital opening in the sternal plate 4 



2. Second legs of male lai'ger than in the female, and with processes. . .Parasitix^. 

 Second legs equal in both sexes 3 



3. The adult is fully chitinized L^laptin^. 



The adult is weakly chitinized Dermanyssin^. 



4. The female genital opening between sternal and genital plates Zerconin^. 



The female genital opening in the sternal plate Uropodin^. 



The group Dermanyssinse has long been 

 recognized, and seems upon appearances 

 to be a natural group, but every character 

 so far suggested to separate it from the 

 Parasitinae or Laelaptinae is hardly of ge- 

 neric value. I have kept it on the un- 

 armed mandibles, but this is but little 

 better than the other characters, and the 

 gi'oup will doubtless have to be merged 

 into the Parasitinae. Michael uses the 

 position of leg I to separate the Uropo- 

 dinae, and this is so much better than 

 the previously given characters that I 

 follow him. 



Oudemans has made several arrange- 

 ments of the genera, one in 11 subfamilies. 

 The characters used are mostly found only 

 in one sex, sometimes the male, sometimes 

 the female, so that it is difficult to use in 

 the identification of specimens. I shall 

 consider that there are 5 subfamilies, 

 which may be tabulated as below: 



The spiracle and peritreme (nearly or quite) on the dorsum; legs short and 



very bristly, all with large caroncles Spinturnicinjs. 



Spiracles and peritremes ventral 2 



No shield or chitinous surface about the anus; parasitic within mammals. 



Halarachnin^. 



A shield or chitinous surface about anus; not parasitic in mammals 3 



First pair of legs inserted within the same body opening (camerostome) as 

 the oral tube; dorsum of body projects beyond the camerostome; genital 

 apertures in the sternal plate; often occurring on insects Uropodin^. 



Fig. lii.— Halarachne americana: s, Sternum of 

 male; t, stigmata and coxae; x, mandible. (Au- 

 thor's illustration.) 



