252 JOURNAL OF SCIENCE. 



I quite agree with Dr. von Jhering that the study of the fresh- 

 water fauna will help us to gain a proper knowledge of the geographical 

 distribution of the organisms during the Secondary epoch as well as for 

 the distribution of land and water during that time. 



Let us now see what relations our land and fresh-water mollusca 

 show to those of Tasmania. The only Unio from Tasmania, TJ. 

 Legrandi, Pett., seems to be closely allied to our TJ. aucAlandica, Gray, 

 but nothing is yet known of the mode of hatching the embryos in the 

 Tasmanian species. The occurrence of Unio in the rivers of the 

 northern part of Tasmania only, as asserted by Messrs. Pettevd and 

 Beddorue, is very interesting, especially from the geological standpoint. 

 Of the very greatest importance in the occurrence of fresh-water shells 

 is the genus Potamopyrgus, which is found in New Zealand and 

 Tasmania only, though Tryon mentions it from Cuba. P. Fischer in 

 his "Manuel de Conchologie," gives only New Zealand as the habitat of 

 Potamopyrgus, and it is also not mentioned in the list of shells from 

 Cuba, If Tryon's notation is correct it coincides with the genera 

 Gundlacliia from Tasmania and Microphysa from New Zealand, ■which 

 both are also found on the Antilles. This would lead to the supposition 

 of a former land communication between Tasmania, New Zealand, and 

 the Antilles ! 



Potamopyrgus is not found in Australia, and there are only two 

 possibilities to account for this fact, viz. : either there was once a direct 

 land communication between New Zealand and Tasmania, or it was by 

 way of Southern Australia ; in the latter case we must admit that the 

 genus Potamopyrgus became extinct in Australia, perhaps by being 

 existent in those parts only which are now submerged. I am inclined 

 to stand to the first theory. The present considerable depth of the 

 Tasman sea is no obstacle to it, and it is a fact, pointed out by several 

 conchologists and observed by myself, that our molluscan fauna is most 

 nearly allied to that of Tasmania. In two papers which appeared in 

 the " Transactions of the New Zealand Institute," vols. 22 and 23, I 

 referred to the close relation between Patula subantialba and P. 

 mutabilis of New Zealand, and P. aniialba and P. Eastbournensis of 

 Tasmania. The genera Phytida, Patula, Pupa, Bulimus, Planorbis, 

 Amphipeplea, Limncea, A nyrfribola. etc , :u-e common to both in many 

 similar forms, and Gundlacliia of Tasmania has no doubt its nearest ally 

 in Latia of New Zealand. We know very little at present of the 

 anatomy of the Tasmanian land and fresh-water shells, except Pota- 

 mojjyrgas, but I am convinced that when it is known, a much closer 

 alliance between the molluscan fauna of both countries will be shown 

 to exist, A further support for my standpoint is shown in the small 

 number of forms common to southern Australia and New Zealand, 

 if we ignore the cosmopolitan genera, which no doubt would be much 

 larger had our former land communication with Tasmania only been by 

 way of Australia. 



The relationship of our molluscan fauna to that of Australia is, as 

 just mentioned, not very great. Besides the cosmopolitan genera there 

 are only Rhytida, Paryphanta, Janella, and Amphibola especially to be 

 mentioned. Of Paryphanta there is only one species (P. atramentaria ) 



