351 



19. Abdoinen without tniiisverse suture. . . . Tkiiyi'ochthonius. 

 Abdomen with transverse suture 20. 



20. Ungues tridactyle. with inner dactyle less than half 



as long- as the others; cephalothorax trnncate in. 



front Parhypochthonii's. 



Ungues either inonodactyle or tridactyle. if tridactyle. 

 dactyles of equal length; cephalothorax not truncate in 

 front Hypochthonius. 



KKY TO THE GENERA OF HOPLODERMID/E. 



1. (ienital and anal openings situated apart; ventral plate 



large Mesoplophora. 



Cienital and anal openings situated together; ventral plate 

 small or rudimentary 2. 



2. Ungues monodactyle; genital and anal covers sepa- 



rate Hoplodekma. 



Ungues tridactyle; genital and anal covers coalescing. 

 Phthiracarus. 



Descriptions of Species. 



Thirty-three species from Illinois are described in the 

 following pages, and of this number twelve are new. In every 

 case the author has made figures illustrating the new species, 

 and a few figures have been made of some of our most common 

 American species. The species are arranged in the natu- 

 ral order under each genus, a key being given to aid in 

 their identiHcation. The genera and families ai-e similarly 

 arranged, the leading characters being given for each group. 



Family ORlBATIDyl^:. 



Forms with the cephalothorax and abdomen immovai)ly 

 fused together: l)ody not compressed; mouth-parts very small; 

 trachea^ o|iening at the acetai)ula of the legs. Abdomen 

 possessing chitinous wing-like expansions called pteromoi pha-; 

 integument usually siiiodth and shiny. Legs never with 

 swollen or iinniilifonii segments. 



