BY W. F. PETTERD. 61 



classification in which to place the many spficies of 

 minute paludiuoidal aquatic shells, so abundant in all 

 our streams and pools, and with this end in view I 

 have selected the most abundant, widely dispersed, and 

 characteristic form for special examination.. Moreover, it was 

 the first species to be recorded, having been discovered in our 

 streams by those illustrious early French naturalists, Quoy 

 and Gaimard. The older conchological writers were satisfied 

 in placing those then known in that, to our modern eyes, 

 mixed genus Faludma which then included a heterogeneous 

 assortment of small shells of a conical form without reference 

 to their habitats being fluviatile or marine. More recent 

 scientists have annexed them to a numerous variety of genera of 

 more or less stable definition ; among others the following 

 generical terms have been applied to many of our indigenous 

 species : — Paludina, Bythinia, Bytliinella, Paludestrina, and 

 Hydrobia, but unfortunately almost all our writers have 

 simply devoted their attention to the outline of the shell and 

 structure of the operculum, few, if any, devoting the amount 

 of attention to the malacological characters that the more 

 modern and elaborate system of classification demands. All 

 scientific conchologists agree that the inhabitant of the shell 

 requires thorough examination before the generical position 

 can be with certainty decided ; more especially in reference to 

 the lingual membrane and the form and arrangement of the 

 denticles thereon. This mixed and varied arrangement can well 

 be overlooked when we consider the lack of information at the 

 disposal of classifiers, for almost the total of the diagnosis 

 that they could give had to be obtained from the extremely 

 limited number of examples contained in the cabinets of the 

 general collector and the cases of museums. My investiga- 

 tions have led me to place, without any hesitation, our most 

 prominent species in a genus quite new for Tasmania or even 

 Australia, it is that of Potaniojnjrgus, established by Dr. 

 Stimpson in the "American Journal of Conchology," Vol. I., 

 1865, for the analogous minute aquatic pulmonate mollusca 

 of New Zealand, having conically ovate shells, horny opercu- 

 lum, animal with long slender tentacles and peculiar formula in 

 the arrangement of the denticles on the membrane. The species 

 have hitherto been supposed to be peculiar to the molluscan 

 province of New Zealand. The most characteristic form 

 of this island (Paludina nicjra, Quoy and GaimardVoyiigo 

 Astrolabe, III., p. 174.) agrees with all the essential characters 

 of Dr. Stimpson's diagnosis of his genus, both as regards 

 outline of shell and animal as well as in the arrangement of 

 the dental formula. Professor Hutton has very concisely 

 worked out the various forms peculiar to New Zealand 

 (Trans. New Zealand Institute, 1882), and that 

 learned concliologist therein refers to the general similarity of 



