12 PUOCEEDIXaS OF THE NATIONAL MVSEIJM. vol. xxviii. 



URIBATOIDEA. 



Cephalnthnrax moval)ly attached to theal)domen; palpi four-jointed. .Hoplodermid.t: 

 Ceplialotliorax not movable; palpi tive-jointed Oribatid.f, 



ix()D(3idp:a. 



No scntiun; no ventral t^hield; niouth-i^arts of adult not prominent from a1)ove; 



no iiulvillns to tardus in adults Argasid.e 



Scutum present; sometimes ventral shields; mouth-i^arts of adult prominent from 



al)ove; pulvillus to tarsus of adults Ixodid.e 



EUPODOIDEA. 



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

 snout-like; cephalothorax with four long bristles above, two in front, two 

 behind; last joint of leg I longer than ])receding joint, often twice as long 



Bdellid.e 



Palpi never geniculate, nor 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.e 



tr():mbidoidea. 



1. Legs I and II with jn-ocesses bearing spines; skin with several shields; coxee 



contiguous C.ECULID.E 



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



2. Palpi much thickened on base, moving laterally, last joint often with two pecti- 



nate bristles; no eyes; leg I ending in several long hairs, adult sometimes 



parasitic Chevletid.e 



Palpi less thickened, moving vertically; eyes usually present; leg I not ending in 

 long hairs 3 



3. Coxfe contiguous, radiate; legs slender, bristly; body with few iiairs; no dorsal 



groove; tarsi never swollen Ervthr.eid.e 



Coxfe more or less in two groups, legs less bristly 4 



4. Body with fewer, longer hairs; often spinning threads; no dorsal groove; tarsi 



never swollen; mandibles styliform (for piercing) Tetraxvchid.e 



Body with many fine hairs or short spines; not spinning threads; often with 

 dorsal groove; tarsi often swollen 5 



5. MandiV)les chelate (for lilting) Trombidid.e 



.Alandibles styliform (for piercing) Rhvxcholophid.e 



HYDRACHXOIDEA. 



Month-parts carried upon a distinct beak; no ventral suckers; living in the sea 



HALACARin.E 



Mouth-parts not carried ujion a beak; usually suckers near the genital openings; 

 usually in fresh water Hydrachnid^e 



Family EUPODID.E. 



The Eupodidie is ti .small family of small mites, several species of 

 which are among our most common acarians. The}- are soft-bodied, 

 delicate mites, with moderatel}' long to very long legs. The body 

 shows more or less distinctly the division into cephalothorax and 

 abdomen; the former usually bears an eye each side; the latter carries 



