508 W. WILLIAMSON AND C. D. SOAR ON BRITISH HYDRACARINA : 



The epimera are about as broad as long, a trifle over 0*7 mm. 

 The lateral expansions are well developed, and the sutures between 

 the epimera are very thick. This applies also to the posterior 

 margins, which are rather broader than usual. The inner edge 

 is nearly straight, having a clean-cut appearance. The width 

 of the fourth pair is nearly equal throughout, the outer edge 

 having -<> ''times a slight concavity near the gland pore, at 

 other times it is slightly rounded. The point where the fourth 

 pair of legs articulates with the epimera lies well in from the edge 

 of the latter, so that about two-thirds of the first segment of the 

 leg lies over the lateral expansion. The recess for the capitulum 

 is about the same length as that for the genital area, but the 

 latter widens out posteriorly. 



The legs are of normal structure, and in the case of the third 

 and fourth pairs may attain to, or even slightly exceed, the 

 length of the body. The terminal segments of the second, third 

 and fourth pairs are distinctly enlarged towards their extremities, 

 but in the case of the corresponding segments of the first pair, 

 if the enlargement exists, it is only weakly developed. None of 

 the legs have swimming hairs. 



The genital area is about 0'23 mm. in length and about 

 0'15 mm. in breadth, and extends for about a fourth of its 

 length beyond the epimera. The lunate plates for muscle 

 attachment which lie at each end of the genital area are fairly 

 well developed. Along the inner edge of each of the valves, 

 there are a number of hair pores. The acetabula are of normal 

 form, and decrease slightly in size from the anterior pair to 

 the posterior pair. The anus is only weakly chitinised, and is 

 without the strong ring observable in some other species. 



Externally, the sexes appear to be hardly distinguishable from 

 one another. 



Nymph. 



Thor's observations on the nymph may be summarised as 

 follows. The length ranges from 0'43 mm. to 0-55 mm., and the 

 breadth from 035 mm. to 0'48 mm., so that the outline may 

 vary from oval to nearly round. The colour is about that of the 

 imago, though sometimes it may be brighter and more trans- 

 parent. The skin is thin and ridged as in the imago. In the 

 nymph, however, the ridges are smaller and not so abundant as 



