THE WATER-MITES (HYDRACARINA) 



865 



29 (28) Genital cleft flanked by two large movable valves, and also ace- 



tabula set free in the body surface. Koenikea Wolcott 1900. 



A beautiful mite of striking form, 

 being greatly compressed and actually 

 concave dorsally; with swimming- 

 hairs. Brightly and variously colored. 

 One widely-distributed species, K. 

 concava Wolcott, adapting itself to 

 varied conditions, and often common. 

 Of small size measuring 0.6 to 0.7 mm. 

 in length. 



FIG. 1334. Koenikea concava Wolcott. 

 Epimeral field and genital area, male. X 65. 

 Inner side, palpus, male. X 278. Side view, 

 capitulum and rostrum female. X 277. 

 (After Wolcott.) 



30 (27) Rostrum short. 31 



31 (36) Suture between the dorsal and ventral plates continuous, completely 



enclosing the dorsal plate, or open posteriorly 32 



32 (35) Acetabula lying near the genital cleft, no modification of leg IV in 



the male 33 



33 (34) Ep. IV quadrilateral in form Mideopsis Neuman 1880. 



A mite of bright colors, with body almost circular 

 in outline, slightly concave dorsally; a short rostrum; 

 swimming-hairs; 3 acetabula on each side, outside of 

 which are narrow, sickle-shaped flaps. One species, 

 M. orbicularis (Miiller), common to Europe and 

 America and widely distributed in this country. Of 

 medium size averaging about i mm. in length. 



FIG. 1335. Midcopsis orbicularis (Muller). Ventral sur- 

 face, female. X 23. Outer side, right palpus. X 123. 

 (Modified from Piersig.) 



Xystonotus Wolcott 1000. 



34 (33) Ep. IV triangular 



Body elliptical; capitulum small and 

 camerostom slightly developed into a 

 rostrum; no swimming-hairs; 3 acetabula on 

 each side, flanked by movable flaps. The 

 genus containing a single species, X. asper 

 Wolcott, known only from two female 

 specimens from Michigan. Of small size, 

 0.61 mm. long. 



FIG. 1336. Xystonotus asper Wolcott. Ven- 

 tral surface, female. X 43- Outer side right 

 palpus. X 195. (After Wolcott.) 



