67 



shells is not Australian, wliicli certainly is most sinjjjulai'; 

 consideriug that the geographical relations of the two places 

 are so close. 'I'hese facts, however, are quite in keeping with 

 the teachings of hoth the zoology and geology of Tasmania, 

 namely, that the island has heeu separated from the conti- 

 nent in Tcry remote periods of the earth'a history, perhaps 

 since the close of the mcsozoic. 



Secondly, we find in the freshwater shells of Tasmania a 

 singularly restricted habitat for some species, and an unac- 

 countably caiiriciuiis distribution for others. Thus some 

 species are only found in small inland lakes, and others are 

 found in one restricted habitat, and then strangely reappear 

 at other and remote parts of the island, while between the 

 two localities there seems to be no present communication. 

 Every species, too, which has a wide range has a local variety. 

 It would seem from these facts that the present physical 

 features of Tasmania have imdergone little change in recent 

 times, but the oiitpouri ng of lavas, etc., in tertiary times, of 

 which there is such evidence^ has altered some of the inland 

 characters, and 30 divided districts which may have been 

 formerly united in their freshwater streams. This, however^ 

 is merely a supposition, which ia only one of many which may 

 be offered in explanation of the phenomena. 



There are in all 32 species of freshwater known shells in 

 Tasmania, that is to say, 28 unitalves and 4 bivalves ; the 

 jiroportion of bivalves to univalves for Britain is 29 to 9. The 

 Tasmanian species are distributed in the following genera : — 

 Physa, 12 ; Limnea, 4; Bythinia, 7; Ancylus, 2; Pomiatopsis, 1; 

 Planorbis, 1 ; Assiminea, 1. The latter is a very doubtfully re- 

 ferred to freshwater, being usually found only in brackish 

 streams. Still, as it seems to live in streams where the tidal in- 

 fluence of the salt water is scarcely felt, I must place the one 

 'J'asraaniau species amongst the list of our freshwater fauna. 



Of the genera, Physa is the largest in number, and this is the 

 case also in Australia, where it takes the place occupied by 

 Limnea elsewhere. But the Australian species are generally 

 very globose with short spires or Avith a peculiar elongation of 

 the penultimate whorl, with a deeply impressed suture, and 

 these features are not marked in the Tasmanian species. 

 Their form rather approximates to the European and American 

 tyix'S. The only exception is in P. ciliata, which has a short, 

 sj.ire, and in the Bruni Island variety a globose habit. Those 

 from Lake Dulverton are not globose. This species is also 

 rein.irkable for being clothed with long reddish hairs in its 

 young state, a feature not seen in any other of its congeners 

 except one from India. It is very strange that this species is 

 only found iu Luke Dulverton and Bruni Island, places more 



