aa. Abdomen not annulate nor prolonged behind; eight legs in the adult stage.
b. With a distinct spiracle upon a stigmal plate on each side of the body (usually ventral) above the third or fourth coxæ or a little behind ([fig. 50]); palpi free; skin often coriaceous or leathery; tarsi often with a sucker.
c. Hypostome large ([fig. 50]), furnished below with many recurved teeth; venter with furrows, skin leathery; large forms, usually parasitic. Ixodoidea
d. Without scutum but covered by a more or less uniform leathery integument; festoons absent; coxæ unarmed, tarsi without ventral spurs; pulvilli absent or vestigial in the adults; palpi cylindrical; sexual dimorphism slight. Argasidæ
e. Body flattened, oval or rounded, with a distinct flattened margin differing in structure from the general integument; this margin gives the body a sharp edge which is not entirely obliterated even when the tick is full fed. Capitulum (in adults and nymphs) entirely invisible dorsally, distant in the adult by about its own length from the anterior border. Eyes absent. Argus Latr.
f. Body oblong; margin with quadrangular cells; anterior tibiæ and metatarsi each about three times as long as broad. On poultry, southwest United States. A. persicus miniatus
A. brevipes Banks, a species with proportionately shorter legs has been recorded from Arizona.
ff. With another combination of characters. About six other species of Argas from various parts of the world, parasitic on birds and mammals.
ee. Body flattened when unfed, but usually becoming very convex on distention; anterior end more or less pointed and hoodlike; margin thick and not clearly defined, similar in structure to the rest of the integument and generally disappearing on distention; capitulum subterminal, its anterior portions often visible dorsally in the adult; eyes present in some species.
f. Integument pitted, without rounded tubercles; body provided with many short stiff bristles; eyes absent. On horses, cattle and man ([fig. 48]). Otiobius Banks.