39 12 Proceedings of the Royal Irish Academy. 



Sub-fam. Diplodontinae. 



Diplodontus despiciens (0. F. MlilL). 



Achill Island ; Westport Eiver ; lakes in the Westport, Belclare, and 

 Louisburgh districts. 



Sub-fam. Hydrarachninae. 

 Hydrarachna scutata Piersig. (Plate I., fig. 9.) 



Lakes at Castlebar, Westport, and in the Louisburgh district. 



Common, and, in company with H. conjecta Koenike, the prevalent forms 

 of the genua found in the Clare Island district, and indeed throughout Ireland 

 generally. 



The shape of the eye-plate varies from the form figured under the name of 

 H. binominata Thor, to the type as described by Piersig (18). 



There seems little doubt that the immature (nymph) form of Hydrarachna 

 which has been described as a separate species, under the name of H. biscutata 

 Thor, is really the nymphal form of H. scutata Piersig. In Ireland it occurs 

 frequently in company with the last-mentioned species ; but never apparently 

 in the adult condition. I have found a series of specimens showing 

 different stages in the development of the eye-plate between the paired 

 (biscut/itu) and the adult unpaired (scutata) condition. One of these is 

 figured, showing the way in which plates of the biscutata form gradually unite 

 in the frontal region, much as sometimes occurs in R. gldbosa (3). 



Some of these nymphal forms were found in Lough Namucka near 

 Louisburgh, and in Garranbawn Lake at Ballynakill, county Mayo, in the 

 month of June by Mr. Fai-ran. 



Hydrarachna conjecta Koenike. 



Common in shallow lakelets at Craigmore and in Creggan Loughs on Clare 

 Island ; Achill Island ; lakes at Westport, Belclare, and Louisburgh. 

 Apparently common throughout the district. 



Hydrarachna distincta Koenike. (Plate I., fig. 10u-c.) 



Lough Avullin on Clare Island ; lakes at Castlebar and Westport. 



I have referred to this species certain specimens with eye-plates, &c, 

 similar to those figured by Piersig in " Deutschlands Hydrachniden " (Plate I, 

 fig. 180c). In his description of this species Dr. Koenike compares it with 



