C. D. SOAR ON THE GENUS HYDRACHNA. 279 



10. Hydrachna thoni, Pier. 



Colour, light red. The nymph only has been found. Length, 

 1*5 mm. Skin covered with sharp-pointed papillae (Fig. 14). 

 Norfolk Broads. 



11. Hydrachna biscutata, Sig. Thor. 



Very similar to H. thoni. The papillae of the skin are also 

 sharp-pointed, but much shorter (Fig. 15). The eye-plates are of 

 a different shape from those of the preceding mite. Mr. Halbert 

 suggests that as this nymph is nearly always found in company 

 with H. scutata, Pier., it may turn out to be the nymph of that 

 species ; but I have certainly taken what I think to be the 

 nymph of H. scutata with one plate only, not the plates as found 

 in H. biscutata. The finding of an adult will settle this point. 

 The nymph only has been found. Lincolnshire and Ireland. 



12. Hydrachna georgei, n.s. 



This species was taken in Osborne Dyke, Norfolk Broads, in 

 1905. It is a small mite, the female being about 2 mm. long. 

 The skin is covered with very fine rounded papillae. The eye- 

 plates are long and narrow (Fig. 16). The genital plate has 

 a very deep narrow bay on the anterior margin. The 

 acetabula are all about one size, none being strikingly larger than 

 the others. The epimera of the fourth pair are much rounded 

 on the posterior edges. I name this species in honour of 

 Dr. George, who, I believe, was the first to write about the 

 Hydrachnidae in England. 



13. Hydrachna distincta, Koen. 



Female about 2*3 mm. in length (Fig. 10). Found in Lincoln- 

 shire. 



14. Hydrachna leegei, Koen. 



Female about 2 mm. in length. Of a very bright red colour. 

 Recorded from England and Ireland. This species may be 

 Journ. Q. M. C, Series II.— No. 63. 21 



