WATSON : RELATION OF MADEIRAN MOLLUSCA TO OTHERS. 3 



There are six species which have been so very recently intro- 

 duced that they can hardly be considered as more naturalized 

 than would any number of species carried over in one's pocket 

 and turned loose in one's garden. These six species are 

 Testacella haliotidea Drap., Helix {Pomatia) aspersa Miill., 

 H. {Patula) rotundata Miill., Flanofbts glaber ]q^., Physa acuta 

 Drap., Hydrobia similis Drap. The removal of these six leaves 

 twenty-eight as the whole number of really native species found 

 in Madeira and which are to be met with elsewhere. Looking 

 carefully at the distribution of these species within the Madeiran 

 area, it is possible with a very considerable amount of proba- 

 bility to divide them into six classes : 



1. Species whose introduction is earlier than all record, 

 but is probably quite recent. These are six in number, viz. :— 

 Arion ater L., Liniax inaximus L., L. flazms L., L. agrestis L., 

 Testacella maugei Fer., Bulimus {Stenogyra) decollatus L. 

 These are sparingly found within human cultivation. 



2. Importations dating from a much earlier period in the 

 five hundred years of human occupation. The seven species 

 of this group are : Limax gagates Drap., Helix {Hyalinia) 

 cellaria Miill, H. [Vallonia) pulchella yinW., Bulimus ventricosus 

 Drap., Zua {Cochlicopa) lubrica Miill., Limncea acuta Draj)., 

 Avcylus striatus Q. & G. These are much more widely dis- 

 tributed, but are still confined to districts occupied by man. 



3. Importations independent of man. This class includes 

 three species the circumstances of whose distribution indicate 

 that they have been long in the islands, while yet they are not 

 where man would have put them. These three are : Achatina 

 acicula Miill., Pupa {Gastrodon) umbilicata Drap., Balea per- 

 versa L. These were probably introduced by natural agencies. 



4. A peculiar class. It includes two species which require 

 fuller criticism. Helix (Xerophila) armillata and Lovea folli- 

 cuius Gron. 



5. Indigenous European species whose birthright is as 

 good in Madeira as elsewhere. In neither can they be called 



