23 20 Proceedings of the Royal Irish Academy. 



48, 49.) The shape of these shells is also different from the type, as 

 they are distinctly more eone-shaped and not cylindrical, but all 

 intermediate forms appear to exist. 

 Clausilia bidentata Strom. — Extremely common on Croaghmore and in several 

 other localities, and shows great variation in size and shape, specimens 

 from the more exposed situations being shorter and more tumid than 

 those occurring on the more sheltered parts of the cliffs. (Plate II, 

 figs. 40, 41, 42.) 

 Balea perversa L. — On my first visit to the island I failed to find this shell, 

 though it was searched for keenly, It turned up afterwards on the cliffs 

 of Croaghmore and Knocknaveen, while a single specimen occurred to me 

 at the Abbey, and Welch took another at the west end. 

 Vertigo antivertigo Drap. — Very common where it occurred, but not so 

 generally distributed as the next two species. Xear the Signal Tower in 

 the bed of a small stream, south slope of Knocknaveen, shore L. Avullin, 

 and X.E. coast. 

 Vertigo substriata Jeffreys. — Widely distributed over the island, but as usual 

 not found in large numbers, nevertheless it is undoubtedly common on 

 Croaghmore, near the Signal Tower with V. antivertigo, and along the 

 south coast. Also taken in moss above L. Avullin, on the X.E. cliffs, 

 and on the south slope of Knocknaveen. 

 Vertigo pygmaea Drap. — Very generally distributed, but nowhere abundant. 

 Two forms were noted : one small and stumpy and of a pale colour, lives 

 on the dry southern cliffs, while a darker and very slender form is found 

 along those of the X.E. coast. 

 Succinea pfeifferi Eossm. — Fine specimens at the Harbour Pool in July, 1911. 

 Frequent in the damper parts of the eastern districts of the island, as 

 round L. Avullin and along the north-eastern coast. Some of those from 

 the Harbour bear shells of a peculiar bronze-green colour - . 

 Limnaea pereger MiilL — A small stunted form is to be found in nearly all 

 permanent water on the island, and fair-sized specimens occur in 

 L. Avullin, Creggan L., the Harbour Pool and one of those forming 

 Lough-na-phuca at the west end. This last " lakelet " consists of about 

 a dozen or more pools, surrounded — and at most seasons, at any rate, 

 isolated from each other — by " Plantago-sward." A small stream Hows 

 through some of the pools, but the majority depend on rain for their 

 supply, and were quite dry in July, 1911. During winter storms these 

 pools must frequently be distinctly brackish, and it is therefore not 

 surprising to find that the majority of the shells are very small and 

 greatly eroded. (Plate II, tigs. 1-7.; 



