18 BEPORT 108^ U. S. DEPAETMEXT OF AGEICULTURE. 



4. Body usually coriaceous, with few hairs; with a speciahzed seta arising from 



a pore near each posterior comer of the cephalothorax; no eyes; mouth 

 parts and palpi ver>' small; ventral openings of the abdomen large; coxae 



all close together; never parasitic; tarsi never with a sucker Oribatoidea. 



Body softer, without such specialized seta 5 



5. Living in water Hydrachnoidea. 



Not living in water 6 



6. Palpi small, tliree-jointed, adhering for some distance to the lip; ventral 



suckers at genital opening or near anal opening usually present; no eyes; 

 tarsi often end in suckers; beneath the skin on the venter are seen rodiike 

 epimera that support the legs; body often entire; adult frequently para- 

 sitic Sarcoptoidea. 



Palpi usually of four or five joints, free; rarely with ventral suckers near 

 genital or anal openings; eyes often present; tarsi never end in suckers; 

 body usually divided into cephalothorax and abdomen; rodlike epimera 

 rarely Adsil)le; adults rarely parasitic • 7 



7. Last joint of palpi never forms a "thumb " to the preceding joint; palpi 



simple, or rarely formed to hold prey; body with but few hairs. .Eupodoidea. 

 Last joint of palpi forms a thumb to the preceding, which ends in a claw (a 

 few exceptions) ; body often with many hairs Trombidioidea. 



SYNOPSIS OF FAMILIES. 



Demodicoidea. 



"With but four legs, of five joints each; living on plants, often in galls. .Eriophyid^. 

 With eight legs, of three joints each; living in skin of mammals Demodicid^. 



Sarcoptoidea, 



1. With tracheae; no ventral suckers; legs ending in claws; body divided into 



cephalothorax and abdomen; the female with a clavate hair between legs 



I and II; not parasitic on birds or mammals TARSoxEMiDiE. 



Without tracheae; no such clavate hair 2 



2. Genital suckers usually present; not parasitic on birds or mammals; skin 



usually without fine parallel lines 3 



Genital suckers absent; parasitic on birds or mammals; skin with fine par- 

 allel lines 4 



3. Legs short, without clavate hair on tarsi I and II; living on insects. .C ANESTRixuDiE. 

 Legs longer, with clavate hair on tarsi I and II; not parasitic (except on 



bees) Tyroglyphid.'E. 



4. Possessing some specially developed apparatus for clingins to hairs of mam- 



mals LlSTROPHORID^. 



Without such apparatus 5 



5. Living on plumage of birds Analgesid^. 



Not on plumage of birds, but on living tissues 6 



6. Vulva longitudinal; in skin and cellular tissue of birds Cytoleiciiid.e. 



Vulva transverse; in skin of mammals and birds Sarcoptid^e. 



Parasitoidea. 



1. Palpi with tlie last joint enlarged ; a spiracle situate above coxa III . .IIolotiiyrid.e. 

 Palpi not enlarged at tip; spiracles situate behind coxa III 2 



2. Genital aperture near the anus; mouth parts retractile within a large buccal 

 cavity, which is situated in an anterior part of the body separated by a suture 



from the rest of the body SrEL^ORHYNCHiD^. 



Genital aperture not or scarcely behind the hind coxae; no anterior mrt of 

 body separated by a suture JParasitid^. 



Oribatoidea. 



1. No division between cojjhnlothorax and abdomen Labidostommatid.e. 



A suture Ixjtwecu ce])lial()lh()nix and abdomen 2 



2. Cephalothorax inovably attached to the al)domen; palpi four-jointed. 



IIoplodermid.e. 

 Cephalothorax not movable: oalpi five-jointed ORiBATiDiE. 



