130 Ayinals Entomological Society of America [Vol. X, 



This genus is erected to include the many nude species, 

 which in the past have been placed in the genus Nothrus, but 

 which differ markedly from the extreme and fantastic type 

 species of that genus, Nothrus spiiiiger Koch. 



Genus Arthrochthonius'" n. gen. 



With the characters of the subfamily Hypochthoninae. Abdomen 

 divided into three or more parts dorsally by transverse sutures, sides 

 strongly depressed, shelf-like, clothed with moderate simple setae. 

 Integument of dorsum of abdomen smooth; body long, pyriform in 

 outline. Cephalothorax without setae above; pseudostigmatic organs 

 very long; legs rather short; claws monodactyle. 



Type species: Ilypochtiiouins paUididus Koch. 



Erected to include many species related to those belonging 

 to Brachychthoniiis Berlese, but having the body longer, the 

 sides strongly depressed, and the integument smooth. 



Genus Steganacarus*- n. gen. 



With the characters of the subfamily Hoplodermatinae. Tarsal 

 claws monodactyle; anal and genital covers separate. Cephalothorax 

 provided with a median dorsal ridge or carina. Abdomen with a hood- 

 like projection extending forward from its anterior margin. 



Type species: Hoplophora anomala Berlese. 



At least one of our North American species, 5. cucullatum 

 (Ewing), is included in this genus. 



Genus Tropacarus''^ n. gen. 



With the characters of the subfamily Hoplodermatinae. Claws of 

 tarsi monodactyle; anal and genital covers separate. Cephalothorax 

 with a median carina above. Abdomen without hood-like projection 

 extending forward from its anterior margin, but with a median carina 

 above like the one on the cephalothorax. 



Type species: Hoplophora carinatum Koch. 



This genus is founded on this peculiar species of Koch's 

 with the dorsal carina on both the abdomen and cephalothorax. 

 I know of no American species which has these characteristics. 



^'From d'pdpov, joint + Chthoniiis. 

 ^^From (TT-yav^s, covered -|- Acarus. 

 ''From rpdiTLs, keel + Acarus. 



