11. — ZOOLOGY, 



Art. XVI. — On the New Zealand Hydrobiinse. 



By Professoe P. W. Hutton. 



{Read before the Philosophical Institute of Canterbury, 3rd November, 1881.] 



Plate I. 



In the " Smithsonian Miscellaneous Collection," vol. vii., and also in the 

 " American Journal of Conchology," vol. i., 1865, Dr. Stimpson founded 

 a new genus — Potamopyrgus — on Melania corolla of Gould, from Banks' 

 Peninsula, and in my " Manual of the New Zealand Mollusca," (Welling- 

 ton, 1880,) I followed Dr. v. Martens in considering this species to be the 

 same as Melania corolla (Eeeve), and Paludestrina cumingiana (Fischer). 

 I also followed Mr. Tenison Woods in putting all oiir other Hydrohiince into 

 Moquin-Tandon's genus Bytliinella. But an examination of these shells 

 during the last year has convinced me that Gould's species is not the same 

 as Paludestrina cumingiana, and that all our species belong to the genus Pota- 

 mopyrgus. I have not seen the " Mollusca of the United States Exploring Ex- 

 pedition," but I found my identification on the fact that P. cumingiana is not 

 found in Banks' Peninsula, and that its dentition does not correspond with 

 the description given by Dr. Stimpson of the dentition of P. corolla, while 

 that description does agree with the dentition of P. fischeri (Dunker), 

 which is common in Banks' Peninsula. The dentition of all the species 

 is so much alilie that all must be included in one genus, but it is necessary 

 to alter Dr. Stimpson' s diagnosis in order to include the slight differences 

 that are found among them. 



The absence of books prevents me feeling certain that all the synonyms 

 I have given are correct, and as three out of the four species vary very 

 much, it is possible that other naturalists may consider some of the forms 

 to be distinct which I consider only as varieties. 



Potamopyrgus, Stimpson. 



Shell, ovato-conic or oval, imperforate ; body whorl more than half 

 the length of the shell ; aperture ovate, the outer lip acute ; peritreme con- 

 tinuous or discontinuous. Operculum horny, subspiral, without any in- 

 ternal process. Animal with the foot rather short, broadest, and slightly 

 expanded, in front. Tentacles very long, slender, tapering and pointed. 

 Eyes on very prominent tubercles. Dentition. Median tooth trapezoidal, 



