Suteb. — Species of the Genus Potamopyrgus. 259 



species to three, and adding a new species (P. pupoides). 

 Hutton says : ' The absence of books prevents me feeling cer- 

 tain that all the synonyms I have given are correct." With 

 regard to books we are not much better off than we were twenty- 

 two years ago, and, besides this, there is the very great incon- 

 venience for us that the types of all the species, Hutton's species 

 excluded, are in foreign museums. It was many years back, 

 when material in my collection was fast accumulating, that I 

 found Hutton's restriction to a total of only four species unsatis- 

 factory. I am fully aware of the great variability of fresh- water 

 molluscs, also of the fact that many species of Potamopyrgus 

 are polymorphic, and therefore one and the same species may 

 have been described under different names. There is a spinous 

 angulate form, then an angulate espinous form, and thirdly 

 an acuminate ecarinate one. Of the New Zealand species 

 only two are polymorphic. 



I tried to get as much information as I possibly could about 

 those species of which I did not possess sufficient knowledge, 

 and I have to thank especially Dr. W. H. Dall, Hon. Curator 

 of Mollusks, U.S. National Museum, Washington ; also Dr. 

 H. Fischer, of Paris : Dr. R. Sturany and Dr. Oberwimmer, 

 K.K. Hofmuseum, Vienna, for the great readiness with which 

 they acceded to my request. The revision now undertaken 

 is to a large extent based on the information thus obtained, 

 and I hope it may prove useful to students of conchology. 



The species of Potamopyrgus described from New Zealand 

 up to now number eleven (omitting crossei, Frfld., ciliata, Gould, 

 and gracilis, Gould, for reasons shown later on), and they were 

 formerly classed under five genera : Melania, Amnicola, Palu- 

 destrina, Hydrobia, and Bythinella. These eleven species I now 

 reduce to five, with three subspecies. 



Genus Potamopyegus, Stimpson (1865) ; Stimpson, Amer. 



Journ. of Conchology, vol. i. (1865), p. 53 ; Smithon, Miscell. 



Coll., No. 201 (1865), pp. 49, 50. 



Type : Melania corolla, Gould, Proc. Bort. Soc. Nat. Hist., 

 vol. ii. (1874), p. 223. 



Synonym : Pyrgophorus, Ancey, Bull. Soc. Mai. France, vol. v. 

 (1888), pp. 188, 192. 



Stimpson' s diagnosis of the genus is reproduced by Hutton 

 in Trans. N.Z. Inst., vol. xiv., p. 143, with some additional re- 

 marks on the dentition. 



Pilsbry says, "Potamopyrgus is a genus of great antiquity, 

 extending at least as far back as the early Eocene. It now 

 comprises all of the fresh- water rissoids of New Zealand, a ma- 

 jority of those of Australia, with species in West Africa and 



