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. [Illustration: 158. (_a_) Tydeus, beak and leg from below; (_b_) Cheyletus pyriformis, beak and palpus; (_c_) beak and claw of Pediculoides; (_d_) leg of Sarcoptes; (_e_) scutum of female of Amblyomma americana; (_f_) leg I and tip of mandible of Histiostoma americana; (_g_) Histiogaster malus, mandible and venter; (_h_) Aleurobius farinæ, palpus and leg I of male; (_i_) Otodectes cynotis, tip of abdomen of male, (_j_) beak and anal plate of Dermanyssus gallinæ; (_k_) palpus of Allothrombium. (_a_) to (_j_) after Banks.] 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. kk. Mandibles chelate, for biting. TROMBIDIDÆ