Oribatei 389 



1-42, 1929. There are many other papers in the Hterature which will 

 have to be studied before critical work can be done on the group, but 

 the above Ust will give a beginner an idea of the group. At the time of 

 this writing very little work has been done on the fauna west of the 

 Mississippi River and this region remains practically unknown. East- 

 ern North America, especially the northeastern region, has been studied 

 to a certain extent by A. P. Jacot who found an influx of some Eu- 

 ropean species. One of these [for example, Scheloribates laevigatus 

 (Koch)] has been reported by Kates and Runkel 1948 from as far 

 west as North Dakota. This species is a well-known German one and 

 is also to be found in Russia. Thus some care must be taken when 

 studying the western forms, and they should be compared with east- 

 ern and European species. This holds true for all mites, both free-living 

 and parasitic. 



Since, as a whole, very little is known of the habits of the oribatids, 

 nothing will be given under the family headings on biology unless defi- 

 nitely known. It is at present sufficient to say that they are generally 

 soil and debris livers and are also to be found on tree trunks, in moss, 

 lichens, and similar habitats, where they feed on the organic matter. 

 Hydrozetes is an exception in that it lives in water. 



Because of the complexities of the divisions created by the Euro- 

 pean workers (cohorts, phalanges, etc.) the group is here presented as 

 a single large unit divided into families only. A few of the families are 

 not so distinct as desired and may, in future time, be recombined. In 

 a few cases certain families have been suppressed but, as a whole, the 

 present family arrangement has been kept, even though morphological 

 characters do not always appear to warrant the divisions. 



Key to the Oribatei i 



1. Mouth parts not visible from above; soft- or hard-bodied 2 

 Mouths parts visible from above; soft-bodied Palaeacaridae 



2. Prosoma and opisthosoma not hinged together 3 

 Prosoma and opisthosoma hinged together (armadillo-like) 32 



3. Genital and anal openings not in common ventral plate; the bound- 

 ary separating these openings close behind genital plates, and 

 anal opening at posterior end of hysterosoma 4 



Genital and anal openings in common ventral plate 5 



1 Based on keys by Sellnick and Willmann. 



