THE MOLLUSCAN FAUNA OF THE OUTER HEBRIDES 275 



THE MOLLUSCAN FAUNA OF THE OUTER 



HEBRIDES. 



By Wm. Denison Roebuck, M.Sc, F.L.S. 



The circumstance that Mr F. Montague Dyke, B.Sc. Lond., 

 of Lower Bebington, Cheshire, spent the months of June, 

 July, August, and September of this year on the Island of 

 Lewis and made such collections of land and freshwater 

 mollusca as his engagements permitted, renders it opportune 

 to bring to a focus such information as we possess concerning 

 the molluscan fauna of vice-county no Hebrides and to 

 embody various hitherto unpublished records from various 

 parts of the archipelago. It is by no means a well-worked 

 area, as an inspection of this paper will show, and it would 

 be of great interest to stimulate its further investigation. 



The group of irregularly-outlined deeply-indented islands 

 known as the Outer Hebrides stretches for about 150 miles 

 in an approximately straight direction from the Butt of 

 Lewis in the north-east to Barra Head in the south-west, 

 with such outliers as the Shiant Islands to the east, Flannan 

 and Monach Islands to the west, and the interesting St Kilda 

 group some forty miles west of North Uist. 



Physically, they are from a conchological point of view 

 barren, treeless, mostly uncultivated tracts of land. Mr 

 Dyke's observations are that the Lewis is one huge peat- 

 bog, and that, with the exception of Unto margaritifer, all his 

 specimens were taken within a mile or so from the shore, 

 which the crofters have cultivated for generations. Practically 

 the whole of the crofting villages are by the coast-line. The 

 crofters clear the peat-bog in preparing their fuel, and then 

 turn over the underlying soil, manuring it well with "tangle- 

 weed" from the shore, and grow their potatoes there. In 

 other parts grass springs up on the cleared land and this 

 becomes the village grazing-ground. Often a very luxuriant 

 growth of grass, clover, etc., is to be found on these grounds. 

 Here it was, near such spots, that he found practically every 

 capture he" made, and, having witnessed the crossing of 



