506 Mr. J. N. Halbert on 
often difficult to distinguish type forms from the numerous 
varieties and aberrations which may be grouped around them. 
As in other freshwater groups, many of the species are widely 
distributed. 
Records of some of the English species have been pub- 
lished by Mr. C. D. Soar *, and I have to thank that gentle- 
man for the loan of types; also Dr. Sig Thor; and especially 
Dr. F. Koenike for his kindness in sending a number of 
valuable type species for comparison. Messrs.C. W. Buckle, 
G. P. Farran, W. F. de V. Kane, 8S. W. Kemp, H. L. Orr, 
and M. 8. D. Westropp have kindly assisted me in collecting 
specimens. 
In the following pages twelve species of Hylats are enume- 
rated, nine of which are referable to known forms, while the 
remaining three are described as new; also two varieties. 
Eylais hamata, Koen. 
1897. Abh. Ver. Bremen, Bd. xiv. pp. 282, 295, fig. 1. 
This species is remarkable for the great length of the eye- 
plate and the relatively small size of the capsules. The 
prevalent Irish form has the chitinous bridge connecting 
the latter either straight or more or less bent backwards, and 
shows no trace of the marginal prominences figured by Piersig 
(Deutschl. Hydrach. pl. xlvi. fig. 168d). However, I have 
seen Dr. Koenike’s mounted types { of this species, and have 
no hesitation in recording the Irish mite as above. 
Fig. 1, 
The eye-plate | of an aberration of this species is figured 
(fig. 1). In this specimen a chitinous process springs from 
* 1900, Soar, C. D., ‘British Freshwater Mites,” ‘Science Gossip,’ 
vol. vii. (n. s.) pp. 203, 204, fios. 1-3 ; 1901, id. ib. vol. viii. (n. s.) pp. 68-70, 
figs. 1-8. 
“+ Dr. Koenike’s slide contains dissections of two specimens: one has 
the pointed prominences on the front of the eye-plate, the other is without 
these, agreeing with the Irish form in every respect. There can be no 
doubt that these two forms belong to the same species, as they otherwise 
agree in structure. 
¢{ With the exception of figure 9 ( X 72) all the accompanying ficures of 
eye-plates are drawn to the same magnification (x 94). Asthey are taken 
from Canada balsam mounts, an allowance should be made for alterationsin 
the outline of the delicate lenses caused by the pressure of the cover-class, 
