46 The Irish Naturalist. 



Slugs, or mollusca without an external shell, are best pre- 

 served in spirits, as the small shell, which is in many forms 

 found under the mantle in the head region, does not afford 

 an}^ very reliable mode of distinguishing the species. 



The collecting of land and freshwater shells might be 

 thought b}^ some to be a rather aimless amusement,- from 

 which little scientific truth could be obtained, but it must be 

 borne in mind that the vast majority of animal remains found 

 fossil in rocks are shells, and that a good knowledge of recent 

 forms will help us to identify the fossil ones. The age of 

 rocks in different places is almost altogether determined by 

 the nature of the fossils contained in them, and, by tracing 

 certain species through a series of geological strata in a num- 

 ber of places, we are able to learn a good deal as to the origin 

 of the species, and the cause of their present distribution. 



One of the most instructive branches of natural history is 

 the study of Geographical Distribution of Animals, and land 

 and freshwater mollusca are particularlj' suitable to elucidate 

 research in this direction, as their migration is very limited, 

 and the}^ are not transported so easily by accidental causes as 

 many other kinds of animals. 



In the preparation of this list of Irish land and freshwater 

 mollusca, I have been very kindly assisted with specimens by 

 Miss Warren, Mr. Praeger, Rev. A. H. Delap, Mr. Barrett- 

 Hamilton, Mr. Ussher, Mr. Redding, Professor G. V. Hart, 

 Mr. H. C. Hart, Miss Sidney Smith, Mr. F. W. Moore, and 

 Mr. Garnett, while Mr. H. C. Levinge was good enough to 

 allow me to collect in his extensive demesne. 



The Roman figures under the heading of each species in- 

 dicate the districts in Ireland in which specimens have been 

 found. The districts, which are those adopted by Messrs. 

 Moore and More in their well-known work the ''Cybele 

 Hibernica," are as follows: — 



I. Kerr^" and South Cork. 



II. North Cork, Waterford, South Tipperar5^ 



III. Kilkenn}^ Carlow, Queen's County. 



IV. Wexford and Wicklow. 



V. Kildare, Dublin, ]\Ieath, lyouth. 



VI. Limerick, Clare, East Galway. 



VII. North Tipperary, King's County, Westmeath, Long- 

 ford. 



VIII. West Galway, West Mayo. 



IX. East Mayo, Sligo, Leitrim. 



X. Fermanagh, Cavan, Monaghan, Tyrone, Armagh. 



XI. Donegal and City of Londonderry. 



XII. Down, Antrim, Derr}^ 



The following is a list of the more important works and 

 papers containing reference to the Irish molluscan fauna, 

 which will be referred to in the text by their numbers : — 



