23 52 Proceedings of the Royal Irish Academy. 



taken alive in this part of the island, and V. costata and P. muscorum are not 

 now known to live on the island at all. The occurrence of V. costata in this 

 deposit is of particular interest, for not only has this species not been found 

 alive on Inishbofin, but it has not previously been found on any of the out- 

 lying islands off the Irish coast. In fact, the only " island " that it has been 

 taken on — Cruit Island in West Donegal — is connected to the mainland at 

 low-water by a broad stretch of sand. Were it not for the fact, however, that 

 V. pidchella is a common resident on these islands, the distribution of its ally 

 would not be of any special interest. 



Shell-Marls. 



Throughout central Ireland few districts will be found which do not 

 contain deposits of marl. This material is a fine creamy substance formed at 

 the bottoms of lakes by decaying vegetation (species of Chara predominating) , 

 shells, other organisms, and particles of calcareous matter. In the district 

 here dealt with there exist near Castlebar and Westport extensive deposits of 

 this material ; but no information is to hand of the shells contained in them. 

 That on the shore of Lakelands Lough near Manulla Junction, in East Mayo, 

 was examined in November, 1911, by E. LI. Praeger and myself. Owing to 

 artificial drainage the level of this lake, like many others throughout the 

 central counties, has been lowered. At the time of our visit the lake was slightly 

 flooded, but was yet some four or five feet below its old level, which was marked 

 by a distinct beach composed of Carboniferous limestone-boulders. Thus the 

 marl was exposed on the flat foreshore, and its upper surface was in places some 

 12 inches above the level of the water in the lake. In some places the marl 

 was covered by peat to a depth of about 2 feet. At the junction of the peat and 

 the marl there was in places a band formed of the compressed rhizomes of 

 Phragmites. Two holes were dug, and samples of the marl from five different 

 levels were obtained, the lowest sample being from a depth of about 5 feet. 

 The depth of the deposit we were unable to ascertain ; it was, however, at least 

 9 feet deep in places. Millions of shells lie around the present margin of the 

 lake, the majority of which are derived from the underlying marl, but these 

 are mixed with many shells only recently dead. 



Among the drift were several species not obtained from the samples of 

 marl, the fauna of which proved to be very poor. 



The list of shells obtained in the drift-material is as follows : — 



Zonitoides nitidus, Succinea pfeifferi, Limnaea pereyer, L. palustris, 

 L. staynalis, L. truncatula, Planorbis alius, P. contortus, Valvata piscitmlis, 

 V. cristata, Bithynia tentaculata, and Pisidium pusUtum. 



