39 26 Proceedings of the Royal Irish Academy. 



extremity. The fourth segment is long '09 mm.), and concave in its dorsal 

 outline PI. II., fig. 21 b). 



The legs are very similar to those of 0. ovalis : they are, however, 

 noticeably longer in the present species. 



Distribution. — Norway, and "West of Ireland. 



Sub-fam. Unionicounae. 



TJnionicola (Atax crassipes (O. F. Mull.). 



Clare Island in Lough Avulliu ; lakes at "Westport, Belclare, and 

 Louisburgh. 



Unionicola gracilipalpis (Viets). 



A female of this species occurred amongst water-plants in Lough 

 Namucka, a peaty lake a few miles from Louishurgh, July, 1910. 



The present species was briefly described by Viets ■ 30 from specimens 

 taken near Bremen. In a subsequent paper 31 the differences between it 

 and the common U. crassipes were fully defined. It may be easily separated 

 from the last -mentioned species by the structure of the palps, which are 

 longer and much more slender ; the chitinous pegs on the fourth segment are 

 much less developed. In the Irish specimens the palps measure T05 mm. 

 in length, agreeing in every respect with Viets' description of the species. 



The legs are slightly longer and more slender in U. crassipes, this being 

 especially noticeable in the case of the first pair : and the pegs on which the 

 long bristles are placed are weaker. Measurement : first pah- of legs, 312 ; 

 second, 373 ; third, "268 ; fourth, -360 mm. 



The eyes are large and much pigmented with black. 



I have also taken this species in Lough Xafin. County Donegal, in the 

 month of September. 



Unionicola rivularis sp. now i Plate III., fig. 32 c-c. 



Westport Paver, June, 1909. 



This is a small free-living species of Unionicola, which appears to inhabit 

 rivers, as the only specimens I have found are from the Pavers Xore and 

 Barrow, as well as from the above-mentioned locality. It is closely allied to 

 ndcola crassipes Miiller, which it resembles in general structure : but is 

 readily distinguished from that species by its much smaller size, and especially 

 by the palp-characters. 



