34] 



The abdomen has the following structures: dorsum, ven- 

 tral plate, anal covers, genital covers, often pteromorpha?, and 

 sometimes large bristles. The dorsum of the abdomen consists 

 of a single large chitinous plate. The ventral plate varies 

 much in size; is sometimes confluent with the dorsum, and 

 contains the genital and anal apertures. The genital aperture 

 is anterior to the anal aperture, and is closed by two chitinous 

 "folding doors", known as the genital covers. The anal aper- 

 ture is similarly closed, its "folding doors" being termed the 

 anal covers. Sometimes on the dorsum, rarely on the ventral 

 plate, long bristles may be found, though frequently the ab- 

 domen is hairless. In some genera, as Pelops and Oribata, there 

 are chitinous wing-like expansions of the abdomen termed 

 pteromorphse (PI. XXXIII., Fig. 4, pter.). 



The legs (Fig. 5) consist of five 

 segments, namely, coxa, femur, 

 genual, tibia, and tarsus. The 

 coxa (Co.), or basal segment, is 

 usually the shortest and stoutest 



Fig. 5. Oribata mollicoma, leg 4. Qf the segments> and som etimeS 



has a blade-like expansion (Bl.) on one side. The femur (Fe.) 

 is usually the largest and sometimes the longest segment. The 

 genual (Ge.) is very small and inconspicuous. The tibia {Ti.) 

 is usually subequal to the tarsus (Ta.), and often bears, espe- 

 cially on the front pair of legs, a long tactile hair at its distal 

 end. The tarsus ends in either one (monodactyle) claw or 

 three (tridactyle) claws, and never in two except in the 

 species Nothrus anauniensis. 



The parts most used for systematic purposes are the 

 pseudostigmatic organs, lamellae, translamella, pteromorpha?, 

 and ungues. 



Internal Anatomy. 



Most of the internal organs of the oribatids may be divided 

 into three systems: the digestive, tracheal, and reproductive 

 systems. The digestive and reproductive organs occupy most 

 of the body cavity. 



