23 44 Proceedings of the Royal Irish Academy. 



The last-mentioned species was taken some years ago in quantity by Mr. 

 "Welch in the Bundorragha River between Doolough and «the sea ; it has not 

 otherwise been reported from West Mayo, except in the adjoining Erriff Valley. 

 Mr. Welch is responsible for the majority of the Doolough species, as he is 

 the only collector who has worked that area. 



The most interesting of the species in the above list is the small dark alpine 

 form of L. arborum which abounds all over Croaghpatrick, even to the very 

 summit, an elevation of 2,510 feet. Attention seems to have been first drawn 

 to this interesting form of the present slug by Dr. Scharff 1 who took almost 

 black specimens at considerable altitudes on Macgillicuddy's Reeks in Kerry, 

 during the year 1899. This variety is not, however, confined to the 

 mountainous areas of the west, as it occurs on Knockdhu, Co. Antrim, 

 associated with arctic or alpine plants such as Arenaria verna and Dryas 

 octopctala, at an altitude of about 900 feet. 



Clew Bay and Castlebar Limestone Area. 



Nowhere in Ireland will the study of the local distribution of the fresh- 

 water mollusca prove more fascinating than in a district situated on the 

 fringe of the central faunal area. 



In some instances, as in West Mayo, this corresponds with the edge of the 

 central limestone plain ; in other districts, as in the north-east of Ireland, this 

 is not the case. In the latter part of the country many members . of the 

 central fauna occupy the greater part of Co. Down, as well as the basins of the 

 Rivers Bann (Lough Neaghj and Lagan. Thus what at first glance would appear 

 to be due to the influence of the limestone evidently cannot be put down 

 entirely to that source. Nevertheless, where limestone areas and non-calcareous 

 and peat-covered ones are contiguous, the line of demarcation of the central 

 fauna is more strongly marked. This is shown clearly in the district -under 

 consideration, and a detailed survey of the lakes and rivers between Castlebar 

 and Clew Bay should prove intensely interesting. Even by the time the 

 boundary of West Mayo is crossed at Castlebar many of the central species 

 have vanished ; 2 among which Planorbis umbilicatus, P. carinatus and t. vortex 

 are most noticeable. 



One species — Neritina fluviatilis — still common at Castlebar, does not 

 seem to cross the watershed between this and the basin of the Carrowbeg ; 



1 See Scharff and Carpenter, Irish Nat., viii, 213-218. 



2 The district hetween Castlebar and the River Shannon is perhaps the least known area in 

 Ireland, iind it is not possible to give at present the exact boundary of these central species. It is 

 possible that some of them do not occur westward of the Shannon basin. 



