THE ACAEIXA OE MITES. 113 



this countn^ and in Europe, are prominent obstacles to successful mushroom culture. 

 Cellars apparently clean in the beginning of the season may be so badly infested by 

 Christmas that crops are impossible. 



It is a difficult problem to destroy tyroglj-phids. Since they have no tracheae, they 

 ai'e not very susceptible to fumigation, although some of them will succumb to pro- 

 longed treatment. Flowers of sulphur and carbolic acid are, at times, of much use; 

 but in many cases destruction of the material attacked is the only remedy. Since 

 many in the hypopial stage are carried by flies, it is ad^^.sable to have the windows 

 screened in all factories where cereals, di'ugs, dried meats, and fruits are prepared. 

 When very abundant the tyrogh-phids are attacked by various predaceous mites, 

 chiefly Cheyhtus and Parasitus, which greatly reduce theii' numbers, and in some 

 cases entirely destroy them. 



Various species have at different times been recorded as temporarily parasitic on 

 man, causing itching and soreness of skin. Persons handling infested products are 

 apt to become attacked, but the mites soon disappear, as they can not breed on the 

 skin. 



^lost of the T^TOglyphidse differ but little in general appearance, and the characters 

 that separate species are often few and minute. The family is usually considered to 

 have affinity to the Sarcoptidae and Analgesidae, but there is more resemblance to the 

 nymphs of the Oribatidae; in fact, oribatid nymphs have been described as Tjto- 

 glyphidae, and \'ice versa. The TjTogljq^hidae have always been J^ept as a separate 

 group, either as a family, or as a subfamily of the Sarcoptidae. Four groups, which 

 may be considered subfamilies, have usually been recognized: Glyciphagus and its 

 allies, Histiostoma, Trichotarsus, and the Tyroglyphus group. Most of the species 

 belong to the last group. The principal genera may be recognized from the following 

 table: 



1. Mandibles not chelate, but elongate and toothed below; body without long 



hairs; palpi enlarged at tip, and proAdded with two divergent bristles. . 



Histiostoma. 

 Mandibles chelate; palpi not enlarged at tip, not with the two bristles 2 



2. Dorsal tegument more or less granular; claws very weak, almost inAdsible, 



some hairs of body plainly feathered; ventral apertures very \a.Tge . .Glyciphagus. 

 Dorsal tegument not granular; claws distinct; no prominent feathered hairs; 



ventral apertures small 3 



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



and abdomen; no sucking genital disks; tarsi long 4 



A clavate or thickened hair on base of tarsi I and II 6 



4. Body without bristles; tarsi without long apical hair, but one at tip of pre- 



ceding joint; a medial frontal projection over mouth parts; genital open- 

 ing large, penis slender, cm-ved Chortoglyphus. 



Body with bristles, no long bristle at tip of penultimate joint of legs 5 



5. Legs with spines; abdomen very bristly above Hericia. 



Legs without spines; living on bees or in their nests Trichotarsus. 



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



between cephalothorax and abdomen Carpoglyphus. 



The bristle on penultimate joint of legs arises from near the tip; a suture be- 

 tween cephalothorax and abdomen 7 



7. Cephalothorax with four distinct and long bristles in a transverse row above; 



tarsi I and II about twice as long as the preceding joint Tyroglyphus. 



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

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

 short 8 



8. Tarsi with some stout spines; caroncle absent 9 



Tarsi without spines; caroncle present ■. Monieziella. 



9. Body very slender; the hind pairs of legs about their length behind the front 



pairs Histiogaster. 



Body robust; the hind pairs of legs but little beyond the front -pairs. .Rhizoglyphu^. 



L 



