SCIENCE- G OS SI P. 



BRITISH FRESHWATER MITES. 



By Charles D. Soar, F.R.M.S. 



(Concluded from page 86.) 



GENUS EYLAIS. 



r I THIS genus, so named by Latreille in 1796, was 

 -*- supposed to contain only one species, Eylais 

 extendens of Midler, until 1896, when Koenike 

 pointed out certain differences in structure, and 

 added to the list of species. This example has 

 since been followed by other writers ; so now we 

 have a large number of Eylais named from different 

 parts of the world. This genus seems likely to be 

 yet further enlarged, for I have two or three 

 specimens which I cannot fit in with Piersig's 

 key or figures. Koch, in his great work, 1835-41, 

 described several species ; but Piersig has placed 

 these under the one name, Eylais extendens. The 

 great point of identification is in the eyes, which 

 are formed in some species very much like a pair 

 of spectacles. 



The characteristics of this genus are : Eyes close 

 together, claws to all feet, fourth pair of legs with- 

 out swimming hairs. 



1. Eylais; diner eta Koenike. 



Eody. — About 3.20 mm. in length and 2.75 mm, 

 in width. Fig. 1, egg-shape in outline, of a bright 

 red colour. The skin of the body is very delicate 

 and easily broken. 



Fie. 1. E.discreta. Dorsal surface. 



Legs. — First pair about 2.40 mm., fourth pair 

 about 3.18 mm., strongly made. The same colour 

 as the body. The first three pairs have swimming 

 hairs, but the fourth pair are quite without them. 

 I do not think this peculiarity is known in any 

 other genus of this family. All the feet have 

 claws. 



Epimera. — In four pairs. Of chitinous struc- 

 ture, rather hairy on the anterior edges. 



Eyes. — The eyes are set in a chitinous plate, 

 joined together with a ridge of chitin. The great 

 difference in the shape of this plate is the principal 

 point of identification in one species from another 

 in this genus. Nearly the whole of Piersig's key 

 is founded on this eye-capsule and eye-bridge, as 



Fig. 2. E. disoreta. Eye-plate. 



he calls it, and he describes twenty-three species 

 known in Germany alone. The eye-plate of this 

 species is shown in fig. 2. In Piersig's key, he 

 says, the fore-rim of the eye-bridge is weakly 

 toothed, the other portion flat and insignificant 

 In the mite I am now describing, I cannot say the 

 anterior edge is as faintly notched as indicated in 

 Piersig's figure of this portion of his mite ; but 

 this may be only a local difference. The exact 

 width across the eyes is 0.41 mm. Several speci- 

 mens were taken and measured, and although the 

 body and leg measurements varied very much in 

 different specimens, the eye measurements came 

 out at about the same dimensions. 



Palpi. — About 1.12 mm. in length. Covered 

 with a number of hairs. Piersig figures a number 

 of palpi of different species, but the difference in 

 their structure is so small that I should not like to 

 undertake to identify any species by that character 

 alone. 



Locality. — Kew Gardens. 



2. Eylais 



Piersig. 



The shape and general description of all the 

 species of this genus are much the same. This 

 one has all the characteristics of the preceding- 

 species, except in size and the shape of the eye- 



ElG. 3. E. soari. Piersig. Eye-plate. 



plate. Length about 2.0 mm., width about 

 1.70 mm. The eye-plate (fig. 3) is about 0.25 mm. 

 extreme width over all. In all the specimens I 

 have examined the eye-plate is about the same 



H 4 



