THE ACAEIXA OR MITES. 



85 



peculiar to rats, produced by a sporozoan, Hepatozoon pemidosus. The sexual 

 cycle occurs within the Laelaps, so that it is a necessary factor in this disease. 



The genera Foecilochirus and Gamasoides are very near Parasitus, but have a mem- 

 branous appendage to the movable finger of the mandibles. Gamasoides has stout 

 spinelike Ijristles aboAe on the femora. 



The genus Parasitus ^ (figs. 160, 161, 162) includes a host of species aU over the 

 world; but few of ours have l)een described, and several are apparently identical with 

 some of the European species. Berlese and others ha^xe split the genus into a great 

 number of subgenera, most of which are difficult to recognize in both sexes. The spe- 

 cies of Parasifj^s (figs. 1(13, 1G4) are mostly found running freely among fallen lea^•es in 

 the woods, or in heaps of refuse or debris. Rarely are they attached to insects or occur 

 in ant nests. Several inliabit sea beaches, often below the high-water marlc. They 

 are always predaceous, and are sometimes beneficial in destroying spiingtails and in- 

 jurious mites. !Most of the species ha^-e the same general habitus, and are difficult of 

 separation. The European forms have been monographed by Berlese. 



I 



Fig. im.—Hyktastcs ovalis. (From 

 Marlatt.) 



Fig. IQl .—Sciulus qvudripilis. (Author's 

 illustration.) 



In Seiulus (fig. 167) are placed many small species, which are quite simple in 

 structure, often with some long bristles; they usually occur in moss, but sometimes 

 on the leaves of plants, rarely attached to insects. They are predaceous in hal)it and 

 feed on tlirips and red spiders. 



Melichares is closely related to Hypoaspis, but the dorsal sliield of the female is slen- 

 der, hardly more than one-half as -wide as the body. 



To the genus Hypoaspis (figs. 168, 169) belong a great number of species, most of 

 which were formerly placed in Jjoelaps. Their hal)its are extremely varied; a number 

 are found in the nests of ants, some attached to the ants, others feeding on the debris or 

 attacking the eggs of the ants; several species are attached to beetles or other insects; 

 others occur in moss, and a few in decaying vegetable matter, or among dead leaves. 

 Berlese has divided the genus into 6 subgenera, depending on the condition of the 

 ventral plates in the female, or on whether the second pair of legs of the male is pro- 

 vided with spurs. These subgenera are Laelapsis, Eulaelaps, Cosnwlaelaps, IJop- 

 lolaelaps, and Androlaelaps . One of our species has been taken in an ant nest, and 

 another (H. placidus Banks) from wet sphagnum moss. 



1 This genus is known to all acarologists as Oamasus, and it is very unfortunate that 

 this name is antedated by the less-known one of Parasitus. 



