Hydrachnellae 



275 



Genera and subgenera: 



1. Hydrovolzia Thor, 1905 



a. Hydrovolzia s. str. 



Type. Polyxo placophora Monti, 1905 



b. Hydrovolziella Viets, 1935 



Type. Hydrovolzia lata Walter, 1935 



2. Acherontacariis Wicts, 1932 



Type. Acherontacarus halacaroides Viets, 1932 



Figure 187 Hydrovolzia placophora 

 (Monti). Dorsum. (After Viets 1936) 



Figure 188 Hydrovolzia placophora 

 (Monti). Venter. (After Viets 1936) 



Discussion: These are nonswimming mites and can be found in 

 springs and brooks of central Europe. 



Rhynchohydracaridae Lundblad, 1936 



Figures 189, 190 



Diagnosis: The body of these mites 4s strongly armored dorsally and 

 ventrally. The dorsal armor consists of a large central and many small 

 marginal shields. Coxal plates i reach far past the anterior end of the 

 body, closing together anteriorly to form a short sclerotized tube; coxal 

 plates I and ii are united. There are no swimming hairs on the legs. 

 Two broad plates surround the genital opening but there are no geni- 

 tal suckers. The palpus does not have spines or protuberances and the 

 chelicerae are long and slender. 



