190 Proceedings of the Royal Society of Victoria. 



In the mollusca proper of the above list there are only three 

 which have not hitherto been recorded from Spring Creek, 

 namely, one lamellibranch which is a new trigonia, the diagno- 

 stic characters of which will be published shortly, and two 

 gastropods. With regard to the representatives of the other 

 classes, the majority also occur at Spring Creek, or in beds 

 belonging to an equally low horizon in the tertiary series. This 

 obviously shows the close relationship existing between the 

 Lower Maude and Spring Creek beds. Upon stratigraphical 

 grounds the Lower Maude beds are evidently very low down in 

 the tertiary series. Our previous work in the Geelong district 

 had led us to suspect that this was also the case at Spring Creek. 



If we look at the results to be obtained from a critical 

 examination of the Spring Creek fossils we have satisfactory 

 confirmation of the above. 



Messrs. Tate and Dennant, in their correlation paper,* record 

 227 species of mollusca, of these we are only able to jDick out 

 three living species which gives a percentage of i.j. One of the 

 above living species, namely, Nucula Grayi^ U Orbigny \^ = Nitcula 

 tuniida, T. IVoods] is, however, not recognised as such by Professor 

 Tate This identification has been made on a careful comparison 

 of the living shells, dredged in Port Phillip Bay, with our fossil 

 species. AVe have been able to add sixty-six molluscan species 

 to the above referred to paper, making a total of 293, without 

 increasing the number of living species, so that it seems perfectly 

 safe for us to assert that the percentage of living species iti these 

 beds is one, or at most, very slightly over. 



As the older basalt overlies beds of this horizon, and is over- 

 laid unconformably by limestones of the Waurn Ponds type, and 

 clays of the Lower Muddy Creek or Mornington type, the two 

 latter conforming to one another with a gradual change in 

 sediment where a junction is seen,t it will ])e of interest and 

 importance to examine the results of the percentage theory as 

 applied to the Muddy Creek beds. Messrs. Tate and Dennant, 

 in the paper above referred to, state: — ^" Out of a total of 725 

 species of all classes from the two well-marked zones at JMuddy 

 Creek, 511 have been definitely traced to the lower beds. Of 



* Trans. Roy. Soc. S.A., 1893. 



t Proc. Ilo}'. Soc. Vic, N.S., vol. iv., p. 11. 



