SCHARFF : ORIGIN OF LAND AND FRESHWATER MOLLUSCA. I4I 



The south-west of Ireland was considered by Forbes to be the 

 district in which the most ancient British living organisms are found. 

 This view is based entirely on the occurrence of certain plants, as no 

 terrestrial animals peculiar to the district were then known to the 

 learned author ; of course we now know that the remarkable slug 

 Geomalacus maculosus inhabits that very region. 



The hypothesis which he offered to account for this interesting 

 flora is that the plants migrated northward in Miocene times from 

 Spain over a land connection which united it with Ireland, and that 

 the great mass of this southern flora was exterminated in Ireland 

 during the Ice Age, the remaining few being the sole relics of 

 this most ancient of our island flora. 



Great advances have been made in our knowledge of the fauna 

 inhabiting the British Islands since Forbes' days, so that we now 

 have better means to revise the deductions formulated by this dis- 

 tinguished naturalist, from a study of the distribution of our native 

 animals. Before doing so, however, it may be of interest to com- 

 pare the views of more recent observers on the origin of our land 

 and freshwater mollusca with those advanced by Prof. Forbes. Dr. 

 Wallace^ while merely repeating Forbes' explanation of the poverty 

 in species of Great Britain, as compared with the continent, and of 

 Ireland as compared with Great Britain, gives us nothing new. In 

 fact he does not even allude to Forbes' recognition of the complex 

 origin of the British fauna, and seems to have given the subject little 

 independent thought. He merely states that the submergence in 

 glacial times destroyed the fauna in the British Isles, and that when 

 England became continental the existing animals entered the country 

 (p. 338). But he thinks sufficient time did not elapse before sub- 

 sidence again occurred, cutting off the further influx of purely terres- 

 trial animals, and leaving us without the number of species which 

 our favourable climate and varied surface entitle us to. Dr. Wallace 

 then proceeds to give us a long list of species and varieties pecuHar 

 to the British Islands, but does not inform us whether they have 

 originated there since the Glacial period, or in what manner their 

 present distribution has been brought about. 



Dr. Kobelt^ regards the fauna of Ireland as an impoverished branch 

 of the EngUsh fauna. He does not beUeve in the pre-glacial origin 

 of such southern species as Helix acuta, H. pisana, If. revelata, and 

 Pupa anglica, or of Geomalacus and Tesfacella, as he presumes none 

 of them have ever been found in pre-glacial deposits. A later immi- 

 gration or even an artificial introduction appear to him more probable 

 (p. 220). 



1 Wallace, A. R., " Island Life," second edition, London, 1892. 



2 KoBKLT, W., " Studien zur Zoogeographie : die Mollusken d. Palaearkt. Region," Wies- 

 baden, 1897. 



