XVIII 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, [xodidae, 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 débris, 
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 Fic. 242.—Oribatid Mites. A, Cepheus ocellatus, 
x 24; B, ventral view of Hoploderma magnum, 
are at present known. closed, x 20. (After 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 
