10 A REVISION OF THE TYROGLYPHID.*. 



3. No clavate' hair on base of tarsi I and II; no suture between cephalothorax . 



and abdoujen; living on bees or in their nests Trichoiarsim. 



A clavate or thickened hair on base of tarsi I and II 4 



4. The bristle on penultimate joint of legs arises from near the middle; no suture 



between cephalothorax and abdomen ('arpogh/jjhus. 



The bristle on penultimate joint of legs arises from near tip; a suture between 

 cephalothorax and abdomen 5 



5. Cephalothorax with four distinct and long bristles in a transverse row; tarsi 



I and II about twice as long as preceding joint Tyroglyphuti. 



Cephalothorax with but two long, distinct bristles (beside the frontal pair), 

 but sometimes a very minute intermediate pair; tarsi I and II usually short 

 and not twice as long as preceding joint 6 



6. Tarsi with some stout spines lihizoglyphus. 



Tarsi with only tine hairs Monkziellu. 



The h3"popiiil stages are known for very few of our forms; it would 

 therefore be of little use to tabulate them. These mites (excepting 

 possibly Trichotarsus) should be studied solely from the mature adult 

 and not described from the hypopial stages. 



Genus HISTIOSTOMA Kramer. 



Mandibles not chelate, but elongate, and toothed below; palpi 

 enlarged at tip and bearing two distinct divergent hairs; a distinct 

 suture between cephalothorax and al)domen; male without anal 

 suckers; tarsi with distinct claws; cuticle not granulate; ventral 

 apertures small; rarely with long bristles on body; no long promi- 

 nent bristle at tip of penultimate joint of legs. 



Type. — H. rostposerratus Megn. {pecthiewn Kramer). 



The peculiar mouth parts of this genus separate it rather sharply 

 from all the other Tyroglj-phida^ It, however, has a well-developed 

 hypopial stage, indicating affinity with Tyroglyphus. The species are 

 variable in habits, but none, so far, has become of economic 

 importance. 



The three species which have been found in this country may be 

 classified by the following table: 



Table of the Species. 



1. Tarsi I four or five times as long as broad ; very slender 2 



Tarsi I scarcely three times as long as broad; body broad, especially 



behind bredpes. 



2. Body about twice as long as broad, with several humps above on the abdo- 



men americanum. 



Body scarcely one and one-half times as long as broad, without humps on 

 abdomen gracilipes. 



Histiostoma gracilipes n. sp. (PI. I, fig. 9.) 



Body hardly one and one-half times as long as broad, sides of abdo- 

 men evenly rounded, and without humps above, emarginate behind; 

 at posterior third of body there is a short curved hair, a similar hair 

 at each posterior corner and on each humerus, and two or three sub- 



