46 THE SCOTTISH NATURALIST 



quite distinct on account of its length and slender form. On 

 the flexor surface in the distal half there are two small 

 protuberances, close together, each with a fine hair at its 

 apex. The fifth segment is small, being little over the 

 length of the first ; it is very slightly curved, and has three 

 minute teeth at its apex. 



The legs increase in size from the first to the fourth pair. 

 The first three pairs end in claws, but the fourth pair have 

 none. Instead, the ends of the fourth pair are tapered, and 

 have inserted laterally one long bristle near the extremity of 

 the leg. The fourth and fifth segments of the third and 

 fourth pairs of legs have a number of swimming hairs 

 arranged in rows. The other segments of the legs have 

 a number of short spines, and at the distal end of a number 

 of the segments there are a few bristles. 



We saw in the genus Thyas that sex dimorphism did not 

 occur. In Limnesia we find it. Here in the female, as 

 above, we have two plates, one on each side of the vulva. 

 The ends are rounded, and the longer sides are weakly 

 emarginate. Each plate has three acetabula, one at the 

 anterior end and the other two closer together towards the 

 posterior end. Scattered over the plate are a number of 

 hairs rising from small papillae. At each end of the plates 

 there is a transverse chitinous ridge whose chief function 

 is muscle attachment. 



In the male the plates are cordate, and have their inner 

 edges concave. The acetabula are about equidistant from 

 one another, and between them, as in the female, are 

 a number of hairs. 



Other Scottish Species of Limnesia. 



Five species of Limnesia occur in Scotland. These are 

 noted in the key to identification appended. The first four 

 are frequently met with, and have all been taken in the 

 neighbourhood of Edinburgh. The fifth is not a common 

 species, and has only been taken by me, so far, in a small 

 ditch near Glasgow. 



