50 



REPORT 108, U. S. DEPARTMEXT OF AGRICULTURE. 



10. 



11 



8. On venter the groove from coxae II reaches the median groove near tip of 



body Frontipoda. 



This groove (when i)resent) reaches median groove near or before middle. . . 9 



9. The grooves from coxae II and III are both rudimentary and neither reach 



near the median groove Rygrobates, Atractides. 



Groove from coxae II reaches median groove 10 



Groove from coxae III also plainly reaches median groove 11 



Groove from coxae III does not reach median groove 12 



Beak with palpi prominent from above; legs arise from margin Arrenurus. \ 



Beak A^th palpi hidden under front of body; legs arise well under body. 



Midea. Midcopsis. 



12. Median groove with a trans\'erse line or interruptions near tip 13 ! 



No such interruptions on median groove 16 



13. Groove from coxae III reaches one-half way to median groove 14 



Groove from coxae III does not reach one-half way to median groove 15 



14. Median groove with line just before ti^:) Wettina. 



Median groove with two interruptione, or at least one much before tip. 



Laminipes, Hygrochoreutes. 



15. In hind legs fifth joint from tip is very distinct Atax. Neuinania. 



In hind legs fifth joint from tip is minute Tiphys. 



IG. Groove from coxae III reaches one-hah way to median groove 17 



Groove from coxae III rudimentary 19 



17. Legs arise from well under body Brachypoda. 



Legs arise near margin 18 



18. Body nearly circular Teulonia. 



Body elongate Curvipes. 



19. A short median process at tip of body Lebertia. 



No such process Axonopsis. 



Fig. 78.— Arrenurus 

 sp.: Palpus. (Au- 

 thor's illustration. ) 



Fig. 79.— Arrenurus sp.: Fe- 

 male from below. (Author's 

 illustration.) 



Fig. 80.— Larva of a hydrachnid. 

 (Original.) 



The genus Limnochares (figs. 72, 73) is practically an acjuatic trombidian; the body 

 is of the same shape, and red in color. It can not swim, but creeps over the mud 

 and plants under water. The young are parasitic on water skaters (Gerridae). Our 

 species is very like the European. 



We have three species of Eylais (figs. 74, 75). They are distinguished by having 

 four simple eyes situate close together on a plate near the median line. They are 

 most frequently found in ponds, and a larva of this genus has been found on mosquitoes. 

 The genus Thyas (figs. 84, 85, 86), of wliich we have a few species, has no swimming 

 hairs on the legs, and beside the lateral eyes there is a median eye in front. About 

 20 species of Arrenurus (figs. 77, 78, 79) have been described from North America; 

 and doubtless many more occur. They are often green in color and have a chitinous 

 dorsum, which, in the male, has a circular furrow open l^ehind. The males have 

 the body extended behind, forming a median ])otiolus. They live most commonly 

 in lakes and ponds. All come from Northern States and none from the far West. 

 Krendowskia and Axonopsis are each represented by one species. Alhia is similar to 

 Amnopsis and the one European species also occurs in the Northern United States. 



