90 PEOVISIONAL AID TO THE STUDY OF TASMANIAJST MOLLUSCA. 



fit the numerous species in Australia, Tasmania, and 

 New Zealand, hitherto variously assigned to Paludes- 

 trina, Amnicola, and latterly Bithynella. It is doubt- 

 ful, however, whether the greatly modified definition 

 may not have the effect of severing some of the 

 original forms embraced uader Stimpson's original 

 definition of Potamopyrgus. A new name, say 

 Huttonia, for the Australian, Tasmanian, and New 

 Zealand forms, with the definition given by Professor 

 Hutton, is suggested as the best course to adopt in 

 the classification of Australasian species determined 

 by the dentition characteristics. 



Genus Beazieeia. Petterd. 1888. (304.) 

 Shell minute, globosely rounded, solid, imperforate; spire 

 small ; body whorl large ; aperture very oblique ; outer 

 lip acute; inner lip thickened; operculum horny, 

 sub-spiral. Animal very similar to Beddomeia Laun- 

 cestonensis, Johnston. Dist.— Fresh water streams, 

 North-Western Tasmania — Eiver Wye, Surrey Hills, 

 and tributaries of the Arthur Eiver. The shell 

 originally described by Tenison- Woods as Ampullaria 

 Tas?nanica, and later transferred to genus Amnicola 

 is here provisionally referred to Petterd's new o-enus 

 Brazieria. 



Sub-Genus Beddomeia. Petterd- 1888. (305-310.) 

 Shell globosely conical, thin, umbilicate or sub-umbilicate ; 

 spire short ; body whorl inflated ; aperture ovate ; colu- 

 mella margin more or less thickened ; operculum horny, 

 pauci-spiral. Animal with a somewhat broad foot ; 

 tentacles long, slender and pointed; eyes sessile at 

 outer, base of same ; muzzle broad and projecting. 

 Dentition as in Potamopyrgus, Hutton non Stimpson, 

 but the trapezoidal median tooth has quite a different 

 arrangement of the inferior basal row, which consists 

 of two ovate elevations on either side of a curved 

 central tooth. 



Formula of denticles on median tooth - — 9UL^ 



2-1-2. 

 Formerly the writer doubted the wisdom of erecting 

 a new genus for the forms now included as above ; 

 but if the difficulty of the alteration of Stimpson's 

 genus Potamopyrgus be surmounted, or if the name 

 Huttonia, as suggested, be adopted for Professor 

 Hutton's new_ definition as applied to Australasian 

 forms, there is little doubt but that the sub-genus 

 erected by Mr. Petterd would be most fitting for 

 Australasian forms of this group. 



