BY FRITZ NOETLIXG, MA., PH D. 129 



species. If it were imported the gigantic marsupials would 

 have existed a considerable time after 1803, because we 

 must assume that it took some time before Physa fontinalis 

 spread from the southern part of the island to its north- 

 western corner. I do not think that anybody would accept 

 such an absurd theory, and we can, therefore, take it as 

 granted that Physa tasmanica is autochthonous. 



On the other hand, if Physa tasmanica and Physa fon- 

 tinalis are really so similar that thev are hardly discernible 

 the pi"oblem becomes very interesting. I hardly think that 

 anybody will assume that Physa fontinalis migrated from 

 the temperate zone of Europe, through the tropics of Asia 

 into temperate Tasmania, without the slightest morphologi- 

 cal change; in fact, if such a migration actuallv took place 

 it would be more probable that the Tasmanian form would 

 be widely different from its European ancestor — unless we 

 believe that having passed the tropics, and reached the 

 temperate zone, it assumed again the shape and form of 

 that, living in the temperate zone on the northern hemi- 

 sphere. 



If such a theory were possible, or even probable, it 

 would revolutionise our entire view of the geographical dis- 

 tribution of animals ; but I think that before it could even 

 hv seriouslj discussed further nroof would be required. 



I rather feel inclined to think that the similarity of the 

 two species represents one of the numerous examples of 

 convergency of form, developing under the influence of the 

 saine climatic conditions. After the disappearance of the 

 glaciers in Tasmania, certain molluscs developed the same 

 tendency towards a certain form, as did similar molluscs 

 in Europe under similar climatic conditions. This is, how- 

 ever, a problem which isi outside the province of this paper. 



With the exception of Bulimus (Caryodes) Dufresnii, 

 the largest land snail of Tasmania, whose eggs could un- 

 mistakably be recognised, and Helix (Flammulina) Hamil- 

 ton! all other species occur in enormous numbers. All 

 these species live at present in Tasmania, and range 

 amongst the commonest species. With the exception of the 

 three species, all the others are fresh water molluscs, but 

 Vitrina Millegani, Helix Hamiltoni, and Bulimus Dufresnii 

 like a moist, cool habitat. 



We must, therefore, assume that the beds in which 

 Nototherium tasmaniense was found are of quite a recent 

 age; in other words, that the gigantic marsupials must 

 have lived in Tasmania up to quite recent times. The 



