167 



Do PORODISCUS INTERRUPTUS AND CRASPEDOPORUS ELEGANS 



BELONG BOTH TO ONE FoRM ? 



By H. Morland. 



(Read July 22nd, 1887.) 



Last gossip night I exhibited a slide containing specimens of 

 Porodiscus interruptus and Craspedoporus elegans, two new species 

 of diatoms described and figured by Messrs. Grove and Sturt in 

 the third part of their paper on the marine diatomaceous deposit 

 from Oamaru, New Zealand. 



In the centre of this slide was a frustule, on one side of which 

 was a valve of P. interruptus, and on the other, one of Craspedo- 

 porus elegans. I am sorry to say that as yet I have only found 

 one such frustule, and thinking it quite possible that one valve 

 might have got jammed into the hoop or "connecting zone" of 

 another valve, I deemed it advisable to examine this frustule 

 critically before finally mounting it, as in consequence of having 

 but one such specimen I could only show it in one position. 

 First I decided upon mounting it showing " side " view, as in such 

 position the two valves could readily be recognized by focussing 

 first on the upper valve and then downwards on to the lower one. 

 Having come to this decision, all that remained for me to do was 

 to examine the " front " view of this frustule, which I had to do 

 11 dry," and under a i-inch objective (285 diameters) ; as far as I 

 could judge, it was a true frustule. However, I still further tested 

 it by passing it in and out of a drop of water (necessary for free- 

 ing it from adherent sand and fragments), and found it behaved 

 exactly the same as I have found other frustules to behave ; but 

 whilst examining it in this manner I had to do so under a lower 

 power, a |-inch, of about 60 diameters. 



The valves of both these forms, roughly speaking, are shaped 

 somewhat like a watch-glass ; in the frustule their convex sides 

 both point one way, Porodiscus interruptus having the convex side 

 outwards, and Craspedoporus elegans having the same side towards 

 the interior. Arguing from analogy only, I should be inclined to 



