28' 



Bithynella, because tlie opercula in specimens examined by 

 liim were partly shelly. I have never met with a shelly 

 operculum in the North. In fact, the Tasmanian species is 

 intermediate between the Littorinidce and Faludinidce. The 

 animal resembles Paludina in the long slender tentaculae, 

 foot, and short linear tongue, of 3 — 1 — 3 denticulated teeth 

 (about 54 rows). It inclines to Littorma in the almost sessile 

 eye lobes, and in the horny pauci- spiral operculum. The 

 species are most variable, according to the altered conditions 

 which affect them. The degree of brackishness has a marked 

 effect uj^on them. B. unicarinata (Tenison-Woods), in the 

 drain near to the Railway Station, has 6 whorls, moderately 

 thick shell, covered with the reddish decomj^osed confervse. 

 About a mile distant, where the water is still more brackish, 

 the same s^^ecies is very delicate pale horn, transparent, 6 

 whorls, and not one-half the size of the larger species. The 

 carina of epidermal membrane is never constant. Sometimes, 

 in awl-shaped hardened spines, as in P. legrandiana (Brazier) ; 

 in interrupted lines, as in Bithynella unicarinata (Tenison- 

 Woods) ; in continuous lines, simjjle ; in continuous or inter- 

 rupted lines, fimltriated ; and most frequently without any 

 apparent carina, as in Bithynella tasmanica (Tenison-Woods), 

 or its synonym, Paliidestrina tvisemaniana (Brazier). In 

 fact, I am inclined to the opinion, as already stated, that the 

 following four shells are merely varieties of one species : — 



Bithynella unicarinata (Tenison-Woods). 

 Faludestrina legraiuliana (Brazier). 

 Ditto wisemaoiiana (Ditto). 

 Bithynella tasmanica (Tenison-Woods). 



And the following may be considered distinct s^^ecies, 

 although they are extremely variable : — 



Bithynella legrandi Ten. -Woods ]st Basin, common. 

 ,, dulvertonensis do. Not seen in the North. 



„ huonensis do. | George Town Heads, Sorell, 



( Circular Head. 

 ,, dunrobinensis do. Doubtful. 



Pomatiopsis striatula Menke Not seen about Launceston. 

 Assiminea tasmanica Ten. -Woods Ditto ditto. 



'Not seen about Launceston, but 

 have received specimens in 

 abundance from Circular 



Planorbis tasmanicus do. A ^^^'\ 7^'%^ ^'^^ -J'^Zi'^^' 



tamed by Mr. T. R. Atkm- 



son. The aperture, however, 



is slightly angled at outer 



I. edge. 



