88 



REPORT 108, tJ. S. DEPARTMENT OF AGRICULTURE. 



discover the food, hasten to it from all sides, and scramble to eat it as fast as pos- 

 sible. By destroying the bacteria and fungi the mites delay decomposition, but can 

 not prevent it. During the past few years many new genera and subgenera have 

 been formed in this subfamily, mainly at the expense of the former Uropoda. The 

 characters are of apparently slight value, and sometimes in only one sex. I have 

 therefore included only a few of them in the following synopsis of the genera : 



2/ 



Fig. 172.— Uroplitella: a, Anal plate; c, camero- Fig. 173.— Uropoda: Caroncle and 



stome; g, genital plate; p, perigenital plate; peritreme. (Author's illustra- 



m, marginal plate; s, spiracle and peritreme; tion.) 



fjventral plate; /, foveae; I, coxa I; II, III, 

 7 F, coxal cavities. (Original.) 



1. Venter provided with impressed foveae for the reception of the legs 2 



Venter without such f ovese 6 



2. Leg I without claws, ending in bristles 8 



Leg I with claws, and caroncle, at tip 4 



3. Body about as broad or broader than long; dorsum smooth Cilliba. 



Body longer than broad; dorsum sculptured or roughened Discopomn. 



4. A perigenital scutum around the genital plate Uroplitella 



No perigenital scutum : :_) 



5. Dorsum smooth or punctured, not sculptured Uropoda. 



Dorsum roughened or sculptured i • 



6. Leg I without claws 7 



Leg I with claws S 



7. Legs with scalelike hairs; dorsal and ventral plates separate and dis- 



tinct Polyaspis. 



Legs without such hairs; no ventral plate Uroseius. 



8. Dorsum covered by one plate fused to the ventral plate; peritreme sinuate; 



anterior coxae contiguous Dinychus. 



Dorsum with several plates not fused to the ventral plate; peritreme but 



little curved ; anterior coxae separate Trachytes. 



9. The anterior part of body, or hood, distinctly separated from the rest of 



the body by a suture Cephalouropoda. 



The anterior portion not separated by a suture Trachyuropoda. 



But few species have been described from this country, although they are 

 extremely common and easily obtainable, and their habits are as interesting as 

 those of any of the acari. Most of the species are found in decajdng matter, as manure, 

 rotton logs, fallen leaves, usually where insects are l)reeding, ha\'ing been carried to 

 the place by these insects. Uropoda (figs. 173, 174, 175) may be divided into two sub- 

 genera — Uroobovella, in which tlie anal plate is more or less distinct from the ventral 



