Article X. — The Oribatoidea of Illinois. By Henry E. 



EwiNG. 



Introduction. 



The mites of the group Oribatoidea, though abundant in 

 this country, have received but little study. About a hundred 

 species have been recorded from America. Out of this 

 number over 90 per cent, are new species, yet with this very 

 large per cent, of new species only two new genera (Gymno- 

 bates Banks and Tumidalvus Ewing) are peculiar to our country. 

 Our fauna is especially rich in the abdominal-winged forms 

 (Pterog aster ea) . The number of the Pterogasterea described 

 from this country, up to the present, is over 40. Nearly all of 

 these winged forms have a shiny integument, which fact may 

 have caused their more ready discovery and the apparently 

 much greater percentage of winged forms here than in Europe. 



The Oribatoidea are appropriately called beetle-mites be- 

 cause of their hard, chitinized integument. They are quite 

 distinct however from the mites of those groups which are para- 

 sites or pseudoparasites of beetles, and which for this reason have 

 been called beetle-mites by some persons. The internal anatomy 

 and life history of this group have been studied very carefully 

 by A. D. Michael, of England, to whom the writer is indebted for a 

 large collection of named European species. The physiology 

 and embryology of the group are almost entirely unknown. 

 Economically the beetle-mites have no great importance. 



The writer is very much indebted to Dr. J. W. Eolsom, of 

 the department of zoology of the University of Illinois, for 

 assistance in many ways. Mr. J. D. Hood, a specialist in the 

 study of the Thysanoptera, has not only collected material for 

 the author from many parts of the state, but has in most cases 

 furnished mounted specimens and also added notes upon their 



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