282 Proceedings of the Royal Society of Victoria. 



common form at present is form iii. ; this, however, is not 

 frequent with the higher thicknesses, 6, 7 and 8, so that in an 

 isolated case of the more advanced form, one can understand 

 that it might not occur with the greatest thickness, as a strict 

 inference would imply. 



H - <i 



Fis. 2. 



