90 



EEPOET 108^ U. S. DEPARTMENT OF AGEICULTURE. 



arise long bristles, and there are also bristles at tip of abdomen. Two other genera, 

 Uropodclla and Fedrizzia, have been described from tropical countries. 



The species of Trachyuropoda are quite variable in appearance, but all have the 

 body longer than broad, with a dorsum showing pits around the edge or else a median 

 depression, or scars, or pits. In many forms the anterior part of the body is nar- 

 rowed and projects forward as a hood over the mouth parts; the margin of the body 

 is often lobed or crenulate; the legs are very short. Several species have been found 

 in the nests of various ants, and they doubtless feed on decaying matter therein. 

 Berlese has divided it into several subgenera, according to the shape and sculpture 

 of the dorsum. 



Superfamily ORIBATOEDEA. 



The oribatid mites may usually be recognized by the 

 presence of a single character — a hair or seta arising from 

 a small pore near each posterior corner of the cephalotho- 

 rax. This pore was formerly considered a spiracle, but 

 it is now known not to be such an organ. Its function, 

 however, is uncertain, and it is called a pseudo-stigma, 

 while the hair arising therefrom is known as the pseudo- 

 stigmatic organ (fig. 178). 



With the great majority of the Oribatidae the tegument 

 is coriaceous; it is because of this that these mites have 

 been called "beetle mites." This name is somewhat 

 misleading, as members of another family, Parasitidae, 

 are often attached to beetles, and therefore sometimes 

 termed "beetle mites." 



The body of an oribatid is short, broad, and usually 

 high. There is always more or less indication, usually 

 very plain, of the division into cephalothorax and 

 abdomen. There is at this point a constriction on the 

 sides, a line or suture on the venter, and a break in 

 the continuity of the dorsal outline. The posterior pairs 

 of legs are apparently attached to the abdomen. The 

 coxae of the legs are arranged in a somewhat radiate 

 manner, and the hind pairs are noA'er remote from the 

 anterior pairs. Each leg is composed of six joints, 

 namely, coxa, trochanter, femur, patella, tibia, and 

 tarsus. Sometimes there is a plate-like expansion near 

 the base of the coxae, known as a " tectopedium." The 

 coxae are usually entirely united to the ventral surface 

 of the body to form a sternal, or, more properly, a coxal 

 plate, each coxa usually being margined by a short furrow. In Nothrus, however, 

 the coxa) may be seen to be quite distinct from the body. On the first two pairs >■< 

 legs the trochanter is extremely small and usually indistinct, while this joint i 

 often very large on the hind pairs. So it follows that the hind legs have, apparcntl> . 

 one more joint than the front pairs. The tarsus is terminated by one or three claw^, 

 but without a sucker or pulvillus. The legs bear a few hairs, but never many; on. 

 at the tip of the tibia is often much longer than the others. The tarsus is commonly 

 more hairy than the other joints. 



On the dorsum of the cephalothorax there are often narrow ridges or lamellae; the posi- 

 tion, shape, and development of these being characteristic of each species. Gencralh' 

 there is an erect lamella each side, extending in a point (sometimes bifid) in front oi 

 the cephalothorax. Frequently there is a translaraolla connecting the lateral lamelhr. 

 There are also on the cephalothorax usually two i)airs of bristles; the pair near and 



Fig. 177. — Dinyclius amcricanus. 

 (Author's illustration.) 



