884 NATURALISED FORMS OF LAND AND FRESH-WATER MOLLUSCA, 



as in the case of Helix fotnatia, L., the Apple snail (somewhat 

 of the appearance of our H. pachystyla\ which was taken to 

 Britain by the Romans and reared in large numbers. Many 

 thousand tons of so-called shell-fish are used per annum as food, 

 in Europe alone, land forms amongst them. 



A case amongst fresh-water shells may also be quoted, in this 

 instance brought about involuntarily. 



Planorhis dilatatus, Gould, an American form, was recorded 

 about 1870 from canals at Manchester, believed to have been 

 introduced with cotton. 



Again, the accidental importation of Dreissena polymorplia, 

 Pallas, the Zebra mussel, probably with timber from the Baltic, 

 proved in a few years as great a pest in one way as the Canadian 

 water weed did in another. 



The forms now found, some of them in abundance, throughout 

 Australasia are, with one exception, from Western Europe. They 

 are as follows : — 



Fresh Water Univalves : — Limncea jieregra, Miiller ; L. 

 stagnalis, Linne ; Planorhis spirorbis, Miiller (?) ; Neritina Jluvia' 

 tilis, Linne. 



Naked Mollusca or Slugs : — Arion ater, Linne ; A . hortensis, 

 Fer. ; A. fuscus, Miiller ; Amalia gagates, Drap. ; Limax agrestis, 

 Linne ; L. flavus, Linn6 ; L. maximus, Linne. 



Shell-bearing Mollusca or Snails : — Zonites cellarius, Miill. 

 Z. nitidua, Miill. ; Helix aspersa, Miill. ; H. nemoralis, Linne 

 H. caperata, Mont. ; H. 2)'>t'lchella, Miill. ; H. virgata, Da Costa (?) 

 Buliimis acutus, Mull. ; together with Helix similaris, Fer., a 

 widely diffused southern species not found in Europe. 



These make up a most interesting list. 



It should be noted that two of the species are very doubtfully 

 Australian, viz., P. spirorbis and H. virgata. The fact that 

 examples of these two species are in the British Museum labelled 

 Australian is insufficient evidence. The former species is from 

 the Cuming collection. The latter was only recorded after a lapse 



