4 Oribatidae 



or somewhat laterally, projects from the dorsal surface of the Cephth.; 

 these two tubes look like stigmata and were formerly supposed to be so; 

 they are now known as the Pseudostigmata (Psstg.), from each a hair- 

 like or flesby organ projects, known as the Pseudostigmatic organ 

 (Psstg. org.) (Fig. 1, 4). The form of this organ varies greatly in different 

 species, and is most useful in identification; the whole apparatus, which is 

 peculiar to the Oribatidae and some few other Acari, is probably an organ 

 of hearing. 



From the Dorso-vertex, between the Psstg., and consequently between 

 the Lam., arise a pair of hairs, often very large; these are the Inter- 

 lamellar hairs (Intlam. hairs) (Fig. 4). 



From the sides of the Cephth. certain blade-like longitudinal out- 

 foldings of the article, not unlike the Lam., are frequently found; there are 

 generally two or more on each side when they are present ; they are some- 

 times prolonged anteriorly and form cusps; their office is to protect the 

 two anterior pairs of legs, which can frequently be bent and pla.ced so as 

 to lie entirely in the deep cavities between these organs which are called 

 Tectopedia (Tectp.) (Fig. 2, 4). 



The Abdomen (Abd.) is usually much larger than the Cephth. its 

 dorsal surface is generally wholly covered by a thick chitinous plate, which 

 usually bends over a little and embraces the edge of the ventral plate. In 

 the Oribatinae the anterior part of each lateral edge of this dorsal plate 

 projects considerably beyond the ventral plate, forming a wing-like organ, 

 more or less flexible, which is capable of slight movement from the action 

 of the muscles of the Abd., not of any special muscles of its own. These 

 wing-like processes are called the Pteromorphae (Ptm.) (Fig. 1, 2). - 

 The genital and anal openings are large and placed in the median line of 

 the ventral plate ; each is closed by a pah' of chitinous folding-doors, called in 

 this treatise the genital covers and the anal covers. - - The expulsory 

 vesicles are two paired sacks in the Abd. of the Nph. of some Oribatidae 

 and in certain other Acari (,,Excretionstaschen"), each of which discharge 

 an excretory fluid to the enterior through a pore in the cuticle. 



The legs are always of five free joints, which are called the coxa, 

 femur, genual, tibia, and tarsus. In some cases the coxae and femora 

 ( or one ^ them) nave a thin blade-like border on their 

 lower edges. The tarsus is ended by a monodactyle 

 (mond.) or tridactyle (trid.) unguis (ung.) without 

 sucker or caruncle. The bid. ung. may be either homo- 

 dactyle (homd.), with all three ung. similar, orhetero- 

 dactyle (hetd.), with the central ung. different from the 

 lateral ones. In one single known instance, i. e. the' 

 European specimens of Nothrus anauniensis, the lateral 

 ung. on one side is abortive leaving a bidactyle (bid.), 

 hetd. ung. The principal parts useful in the identification 

 of species (in addition to the general shape and appea- 

 rance) are the Psstg. org., the Lam., the Intlam. hairs, 

 the Trlam., the Ptm., and the ung. 



Oribatidae have been found in all parts of the world. 

 Oribata mollicoma. , . , , , 



Lee 4 f 180 ") which have yet been searched for them; they vary extremely 



little in different countries the distribution being remarkably wide. 



Xo genera are known from Tropical America which are not known in Europe, and 

 the species from Franz- Joseph- Land are either identical with, or closely allied 



