114 



REPORT 108^ U. S. DEPARTMENT OF AGRICULTURE. 



The hypopi of the various genera, as far as known, can be separated by the following 

 table: 



1. A pair of clasping organs on venter near tip of body, margins not sharp- 



edged Labidophoriis . 



No clasping organs, but an area of suckers 2 



2. Anterior legs end in very large claw; margins of body not sharp-edged. . Trichotarsiis. 

 Claws small or of normal size 3 



3. An eyelike spot each side of anterior part of body Histiogaster. 



No such eyelike spots _ ^ 4 



4. Venter behind with a submarginal crescentic plate; tarsi rather long Hericia. 



No such crescentic plate 5 



5. Legs very slender, especially the tarsi; hind legs often bent ioTwsiTd. . Eistiostoma. 

 Legs much shorter, the tarsi not slender 6 



6. Five pairs of suckers in the plate arranged 2-2^-2 _ AleuroUus. 



Suckers not in such arrangement Rhizoglyphus and Tyroglyphus. 



Fig. 'iZb.—AleuTohius farinne . 

 b, leg I of male; c, palpus, 

 (Author's illustration.) 



a, Venter of male ; 

 ', tarsus IV of male. 



Fig. 230. 



Tyroglyphus lintTKri : Female. (Author's 

 illustration.) 



About five species of Ilistiostoma are known from the United States. They differ 

 in length of legs and in shape of body. Some occur among dead loaves, others under 

 bark with decaying matter. Their hypopi are often very abundant and have very 

 slender legs. The hypopial stage of one (//. muscamm Koch) is often attached to 

 house flies; another species, //. ajnericanuin Banks (figs. 229, 230, 231), was taken under 

 bark, which was also infested ^\'ith a Bhizoghjphus. This species has a number of 

 humps on the dorsum of the body, and upon the summit of each is a small hair. In 

 Eur()])e one species lives in mushrooms and s])reads a disease that causes the decay 

 of the pileus. Nearly all the species occur in dccajing material, but Jensen has 



