276 C. D. SOAR ON THE GENUS HYDRACHNA. 



7. Eye-plate short and broad and gently curved towards median 



line on the outside posterior margin of plate ; ends of 



plate much rounded (10. H. thoni). 

 Eye-plate short and broad, the outside line bowed inwards 



towards posterior margin (11. H. biscutata). 

 Eye-plate long and narrow, the inside edge of each plate 



forming one curve towards median line (12. If. georgei). 



8. Eye-plate with a square projection on outside edge of each 



plate ; posterior ends of plates tongue-shaped (13. H. dis- 

 tincta). 



9. Ridge short, commencing on inside margin of each eye, and 



extending only a short distance backwards (14). H. leegei. 

 Ridge short, placed just behind each eye (15. H. maculifera). 

 Ridge extending from between the eyes to about the same 



distance backwards as eyes are wide apart ; ridge much 



bent (16. H. comosa). 

 Ridge very long, anterior portion straight ; posterior portion 



curved and extended outwards (17. H. bivirgulata). 



10. Body colour light red (10). 

 Body colour very dark (11). 



11. Mite large, about 5 mm. long, with two small ridges just 



behind the eyes and two gland-plates farther back, the 

 whole forming nearly a square (18. H. halberti). 

 With gland -plates only, one behind each eye a little farther 

 back than breadth of eyes (19. H. ivilliamsoni). 



12. Mite small, with two small chitinous ridges just behind the 



eyes, and two gland-plates well behind (20. H.fuscata). 

 Mite large, similar to above, with the chitinous ridges or 

 muscle attachments about half-way between the gland 

 plates and the eyes (21. II. incisa). 



1. Hydrachna levigata, Koem 

 This mite was described by Dr. Koenike in the Zoologischer 

 Anzeiger, in 1897. It is easily identified, being, as far as is at 

 present known, the only species of Hydrachna with a smooth 



