METASTIGMATA 467 



Sub-Order 3. Metastigmata. 



The four families which constitute this sub -order comprise 

 a large number of Mites in which the tracheae open near the 

 articulation of the legs, and consequently in a somewhat posterior 

 situation. The families are Oribatidae, Argasidae, Ixodidae, and 

 Gamasidae. 



Fam. 1. Oribatidae. The Oribatidae or "Beetle-mites" are 

 free-living Acari, with tracheae of which the stigmata are con- 

 cealed by the articulation of the legs. The cephalothorax is 

 distinctly marked off from the abdomen, and bears dorsally two 

 " pseudo-stigmatic " organs. The rostrum is inserted below the 

 cephalothorax. These Mites gain their popular name from the 

 beetle-like hardness of their integuments. They are oviparous or 

 ovoviviparous. Eyes are always absent. 



These are small creatures, seldom attaining the twentieth of 

 an inch in length. They are vegetable-feeders (except, perhaps, 

 Pelops}, and are to be found in dead wood or vegetable debris, 

 under bark, or among moss and lichen. In winter they often 

 take refuge under stones. It is impossible at present to estimate 

 the number of existing species, for only a few localities have 

 been systematically worked for them, and their small size has 

 prevented their inclusion, in any numbers, in the collections of 

 scientific expeditions. Our knowledge of the group is likely, 

 however, to be largely extended, for it has been found that they 

 reach England alive and 

 in good condition from the 

 most remote regions if 

 moss or other material in 

 which they live is collected 

 when not too dry, and her- 

 metically sealed up in tin 

 cases. 



About twenty genera 



and more than 220 species FIG. 242. Oribatid Mites. A, Cepheus ocdlalus, 

 . -, x 24 ; B, ventral view of Hoploderma mai/ni'm, 



are at present known. closed> x20> (Alter MichaeL) 



Pelops has much elongated 



chelicerae, with very small chelae at the end. There are ten 



species, found in moss and on bushes. Oribata numbers about 



fifty species, found in moss and on trees. Notaspis, in which the 



