gg. Legs I and II without such processes; few if any shields.
h. Palpi much thickened on the base, moving laterally, last joint often with two pectinate bristles; no eyes; legs I ending in several long hairs; adult sometimes parasitic. Cheyletidæ
Cheyletus eruditus, which frequents old books, has once been found in pus discharged from the ear of man.
hh. Palpi less thickened, moving vertically; eyes usually present; leg I not ending in long hairs.
i. Coxæ contiguous, radiate; legs slender, bristly; body with few hairs; no dorsal groove; tarsi not swollen. Erythræidæ.
ii. Coxæ more or less in two groups; legs less bristly.
j. Body with fewer, longer hairs; often spinning threads; no dorsal groove; tarsi never swollen; mandibles styliform (for piercing). Tetranychidæ
The genus Tetranychus may be distinguished from the other genera occurring in the United States by the following characters: No scale-like projections on the front of the cephalothorax; legs I as long or longer than the body; palp ends in a distinct thumb; the body is about 1.5 times as long as broad. T. molestissimus Weyenb. from South America, and T. telarius from Europe and America ordinarily infesting plants, are said also to molest man.
jj. Body with many fine hairs or short spines; not spinning threads; often with dorsal groove; tarsi often swollen.
k. Mandibles styliform for piercing. Rhycholophidæ.