LAND AND FRESHWATER MOLLUSCS OF INNER HEBRIDES 19 



THE LAND AND FRESHWATER MOLLUSCS OF 

 SOME ISLANDS OF THE INNER HEBRIDES. 



By N. Annandale, D.Sc, F.A.S.B., F.R.S.E. (Zoological 

 Survey of India). 



The specimens on which these notes are based were col- 

 lected in August 192 1 by Mr Noel Smith, Mr C. M. Yonge, 

 and myself, mostly on certain small islands off the west coast 

 of Mull, with a few on the adjacent parts of Mull itself The 

 islands visited were Ulva, which was our headquarters for a 

 month, Innis Kenneth and Eorsa, all lying in or just outside 

 Loch-na-Kael, and lona, situated some fifteen miles to the 

 south-west of Ulva off the Ross of Mull. Our collection 

 from Ulva is naturally larger and more complete than that 

 from the other islands, to which we paid more hurried visits. 

 From a geological point of view the four smaller islands 

 fall into two pairs, and with their structural peculiarities it is 

 possible to correlate distinct differences in the molluscan 

 fauna. Ulva, Innis Kenneth, and Eorsa lie within a radius 

 of five miles, but Innis Kenneth differs materially from the 

 other two in the character of its rocks and soil, and also in its 

 flora and fauna. Mr Smith found on it several plants that 

 do not grow on Ulva, while Mr Yonge observed differences 

 in the Coleoptera. Of the differences in the molluscan fauna 

 I will speak presently. In certain respects the island agrees 

 with lona. The physical differences between the two pairs 

 of islands are these — Ulva and Eorsa are composed of Tertiary 

 basalt and have no deposits of sea-sand, their shores being 

 rocky and muddy. The scanty and peaty soil that clothes 

 the basalt is for the most part water-logged up to the tops of 

 the hills, one of which on Ulva reaches a height of just over 

 1000 feet. On lona and Innis Kenneth, on the other hand, 

 the soil, which consists largely of shelly sand, is abundant 

 and dry except at marshy spots. The rocks, which play a 

 less important part in the structure of the surface, are varied, 

 but in themselves are evidently of little moment in the 

 ecology of the molluscs. It is the nature of the soil that 



