THE ACAKIXA OE MITES. 19 



IXODOIDEA. 



1. No sciitiim ; no ventral shield ; mouth parts of adult not prominent from ahove ; 



no pulvillus to tarsus in adults Argasid^. 



Scutum present; sometimes ventral shields; mouth parts of adult prominent 

 from above; pulvillus to tarsus of adults Ixodid.e. 



Trombidioidea. 



1. Legs I and II with processes bearing spines; skin with several shields; coxae 



contiguous _ C^cuLiD^. 



Legs I and II without such processes; few, if any, shields 2 



2. Mandibles chelate or uncinate, that is a basal rather thickened part, with a 



claw near its tip 3 



Mandibles stylate (needlelike), and retractile; coxse in two groups 4 



3. Tarsal joint of leg I usually enlarged; usually a crista metopica on cephalo- 



thorax; coxae in widely separate groups Trombidhd^. 



Tarsal joint of leg I not enlarged, often long; no crista Tnetopica; coxae usually 

 in one group, contiguous Anystid^. 



4. Tarsi enlarged; usually a dorsal groove; adults free Erythr^id^. 



Tarsi not enlarged ; no dorsal groove 5 



5. Phytophagous, occiuring on plants; often spinning threads; palpi simple; leg 



I never ending in long hairs; all legs with claws; bristles usually simple. 



TeTR ANYCHID^ . 



Predaceous or parasitic, often on birds or mice; palpi often enlarged at base 

 and forming a forceps; claws often absent from one or more pairs of legs; 

 often with pectinate bristles Cheyletid^. 



EUPODOIDEA. 



Palpi simple ; mouth parts hidden by a hood ; no apparent division of body, 

 and no bristles above; last joint of leg I but little longer than preceding. 



Crypto GXATHiPuE . 



Palpi often geniculate, or else fitted for grasping prey; mandibles large and 

 snouthke; cephalothorax with four long bristles above, two in front, two 

 behind; last joint of leg I longer than preceding joint, often twice as long. 



Bdellid^. 



Palpi never geniculate, not fitted for grasping prey; beak small ; cephalothorax 

 with bristles in different arrangement; last joint of leg I shorter or but little 

 longer than preceding joint; eyes, when present, near posterior border. 



EUPODID^. 



Hydrachnoidea. 



Mouth parts carried upon a distinct beak; no ventral suckers; living in the sea. 



Halacarid^. 

 Mouth parts not carried upon a beak; usually suckers near the genital open- 

 i ings; usually in fresh water Hydrachxid.^. 



If one desires to use suborders, three of these may be recognized, as follows: 



1. With a distinct spiracle on a stigmal plate on each side of body near the third 



or fourth coxa; palpi free; skin often coriaceous; tarsi often with sucker; 



rarely any distinct eyes Mesostigmata. 



Ko such spiracles or stigmal plates 2 



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



genital or anal apertures; eyes usually present; tarsi never end in suckers; 



body soft; adults rarely parasitic Prostigmata. 



Palpi small, rarely more than three-jointed, often hardly \dsible; often with 

 ventral suckers; never with eyes; body often hard, if soft then showing 

 rod -like epimera to support legs, and often parasitic Cryptostigmata. 



The ^Mesostigmata includes the Ixodoidea and Parasitoidea. The Prostigmata 

 includes the Eupodoidea, Trombidioidea, and Hydrachnoidea. The Cryptostigmata 

 includes the Oribatoidea, Sarcoptoidea, and Demodicoidea. 



