39 4 Proceedings of the Royal Irish Academy. 



occur. The following would seem to belong to this peat-moor fauna : — 

 Thy as vigilans Koenike, Pionacerus Leuckarti Piersig, Arrhenurus Nemnani 

 Piersig, and possibly Oxus plantaris Sig. Thor, and Lebcrtia fivibriata Sig. 

 Thor. 



Some interesting problems are concerned in the past history of the 

 fresh-water fauna of the Clare Island district. It is generally agreed that 

 the area of the island formed part of the mainland in former times, so 

 that a Hydracarid fauna was doubtless established there. We are assured 

 by those who have studied the evidences of ice-action that the district 

 must have passed through a period of severe glaciation. This Ice Age is 

 believed by some to have existed subsequent to the separation of the 

 island from the mainland; so that, if the ice exterminated the fresh-water 

 fauna, it must have been reintroduced in some way. On the other hand, 

 it has been urged from the evidence supplied by the occurrence of peat bogs 

 that are now partly submerged under the sea that the island may well 

 have been united with the mainland after the cold period. 



With regard to the extermination by ice of the original Hydracarid 

 fauna, one can only say that, had the conditions been so severe as has been 

 supposed, the survival of a water-mite fauna resembling the present one would 

 have been impossible, especially as regards those species that inhabit water 

 of a higher temperature (eurythernial forms). With those that inhabit 

 low-temperature waters (stenothermal forms) the case is not so clear, as 

 these forms reach their highest development in northern and alpine regions ; 

 indeed Dr. Zschokke, who has carefully studied the stenothermal forms, 

 believes that they are relics of the Glacial Age. 



The dispersal of the fresh-water mites is closely concerned with their 

 larval stage, when they attach themselves to various winged aquatic insects. 

 It is chiefly through the agency of these temporary hosts that they are 

 carried from place to place, and in course of time reach the most remote 

 localities. Numerous winged aquatic insects are found on Clare Island and 

 throughout the neighbouring district — such are species of Dytiseus, Agabus, 

 Xotonecta, Nepa, and Corixa, all favourite hosts of Hydracarid larvae. One 

 would imagine, however, that the wings of such insects as Notonecta, Corixa, 

 and other aquatic Hemiptera are more suited for comparatively short flights 

 than for facing a sea-barrier of from 3 to 14 miles over which sweeps an 

 opposing westerly breeze. 



In the case of Dytiseus and Agabus, however, the island must be con- 

 sidered as being in the " danger zone," as it is quite possible that these 

 comparatively strong fliers do occasionally cross from the mainland with 

 Hydracarid larvae attached to their bodies. 



