168 ON PORODISCDS INTERRUPTDS AND CRASPEDOPORUS ELEGANS. 



think that this diatom is, or was, a parasitic form, growing some- 

 what after the manner of the Cocconidece, Craspedoporus elegans 

 being underneath. 



As tending to confirm my observations of this frustule, I may 

 add that since I mounted it I have found a valve of Craspedo- 

 porus elegans with the " connecting zone " still attached, the same 

 being on the convex side of the valve, in a similar relative position 

 as in the frustule. 



Should other diatomists examining this deposit be so fortunate 

 as to find frustules of these forms, either confirming or refuting 

 my views, I shall be glad if they will favour this Club with 

 information respecting the same. As, however, these forms are 

 scarce, it is possible we may have to wait some time before 

 receiving such information ; when valves are scarce, perfect 

 frustules are still scarcer. 



The present is, I think, a good example of how difficult it 

 is to correctly describe a fossil diatom when the same is not 

 represented by living specimens. The Oamaru deposit, from 

 which I obtained my specimen, contains also another diatom, of 

 which the frustule has dissimilar valves. I refer to Trinacria 

 ventricosa. At first sight these valves would be considered as be- 

 longing to totally different species, but, fortunately, as this form is 

 rather common in the deposit, complete frustules, with the two 

 dissimilar valves in situ, are to be found without much difficulty. 



