No. 2394. NEW NEARARCTIC SPIDER MITES— EWING. 661 



Genus BRYOBIA Koch. 



Two species of this genus, B. pratensis Garman and B. pallida 

 Garman, have been described in the past as new from the United 

 States. The description of B. pallida was soon recognized as being 

 based on immature individuals of B. pratensis; but for many years 

 in this country the name, B. pratensis, has been held valid, being the 

 scientific designation of our common brown mite, or so-called clover 

 mite. Prior to the year 1911 the present writer sent a specimen of 

 B. pratensis to Dr. A. C. Oudemans, the noted Dutch acarologist, for 

 comparison with European forms. As a result of his comparisons 

 he decided that our B. pratensis was only a synonym of B. cristata 

 Duges. This is the synonymy which he gives in a printed article 

 published in the same year. 



In 1914 Ivar Triigardh, a Swedish authority, published the results 

 of his extended taxonomic study of the genus Bryobia. In his 

 English summary he gives the following pertinent statement in regard 

 to synonymy in the genus : 



All the different species described by Koch, G. Canestrini, F. Fanzago, Berlese, 

 Thomas, and Garman under the name of praetiosa, speciosa, nobilis, gloriosa, ribis, 

 and pratensis, must be referred to praetiosa Koch, being mere variations and different 

 instars of that species. 



Triigardh for the first time ascertained the variations due to growth 

 in the old species of Koch, as well as the individual variations found 

 in the adults of the same species; and as a result of this has not only 

 given us his very valuable list of synonyms, but has shown to what 

 extent one can depend upon such variable characters as must be 

 used in specific diagnosis. For the present it appears it is better to 

 confine all descriptions of new species to adult, egg-bearing females. 

 The variations, which are very great in the genus, must be worked 

 out later for the different species. 



There has accumulated in the United States National Museum a 

 large number (many hundreds) of Bryobia specimens from almost all 

 parts of the United States. A survey of this material shows, after 

 eliminating variations due to growth by confining examinations 

 exclusively to adult females, and after making all due allowances for 

 individual variations noted by Triigardh, that one can recognize at 

 least three forms here. One of these, the common brown mite, B. 

 praetiosa, is distributed over most of the country and appears to be 

 the only species found east of the Mississippi River. Beisdes this 

 form there occurs in the west another and in the southwest a third. 

 The differences between these are, in the writer's opinion, of specific 



