The Specific Name of the Australian Aturia. 



18. 



possess a larger comparative series of the Australian form, that 

 view^ might undergo some modification, and it is to be regretted 

 that Mr. Newton did not have time to critically examine the 

 series of Aturia in the Melbourne National Museum." 



From a re-examination of the Australian examples I am . 

 satisfied that the forms are perfectly distinct, the compressed 

 sides and the generally narrower shell, being marked characters 

 of Balcombian, Janjukian and Kalimnan specimens. This fea- 

 ture of the compressed shell is very characteristic of all the 

 southern specimens so far as I have seen, and in some specimens 

 it is developed to an extreme degree. On the other hand the 

 European A. atari tends towards obesity, and an extreme ex- 

 ample of this is figured by Bronn.'^ 



Hypothesis of Type Origin. 



From the preceding note of the variations seen in the southern 

 and northern forms it is highly probable that the early ( ? Lower 

 Oligocene or even Eocene^) shells which were ancestral to- 



Or/\u /\spect of Northern /^nq Soot hernty pes. 



6. Newton and Cricks' agreement as to the identity of the two forms. 



7. Lethaea Geognostica, Vol. iii., and pi. xHi., figs. 17a-e. 



8. This earlier stage is suggested on account of the occurrence of large^- 

 and well-developed shells in the Balcombian of Muddy Creek, one example,, 

 found by my son, W. D. Chapman, and now in the National Museum, having-, 

 a diameter of nearly seven inches. 



