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THE SLUGS OF lEELAND. By R. F. SCHAEFF, Ph.D., B.Sc, Keeper of the 

 Natural History Museum, Dublin. Plates LVI. & LVII. 



[Eead Makch 9, 1891.] 



The term "Slug," used in the ordinary sense, is applied to snails without an 

 external shell. Anatomically, the slugs cannot be grouped into one distinct family 

 apart from the snails. Even of the few genera inhabiting Ireland, Limax, 

 AgrioKmax^ and Amalia must be placed in one family with the Helices, to which 

 they are much more closely related than they are to Arion and Geomalacus, the 

 two other Irish genera of slugs. 



From a systematic jDoint of view a description of these animals, leaving 

 unmentioned the closely-related snails, may seem rather unscientific, but this work 

 has been undertaken chiefly with a view of solving some of the difficulties regarding 

 the distribution of terrestrial animals ; and land snails having been known to be 

 transported by sea, as has been shown by Darwin [Origin of Species, 6th ed., 

 p. 353), are of less importance in this respect than slugs. The sea, which is the 

 principal means of communication for other animals and plants between mainland 

 and island, forms an almost impassable barrier for slugs, sea-water being deadly 

 both to their eggs and themselves ; therefore, if we find the slugs of mainland and 

 island agreeing in anatomical characters, we may generally conclude that the 

 island must have had a land connexion with the mainland at some time or other, 

 and the more closely related the forms are, the more recent must have been this 

 connexion. 



The slugs of Ireland are very closely related, and in most cases are identical 

 with those on the Continent of Europe. It is not my intention, however, to 

 enter in this Paper more fully into the cause of the geographical distribution of 

 slugs, as I propose to deal with the question in a subsequent communication. 



Until quite recently, the tongue, or radula, of Mollusca has formed one of the 

 chief characters in the classification, and the separation of one species from anotlier. 

 Specific distinction was based almost entirely on external characters and on 



TRANS. EOT. BITB. SOC, N.S. TOT.. IV., PART X. 4 C 



