696 SUMMARY OF CUERENT RESEARCHES RELATING TO 



certainly be able to celebrate its centenary if it is left on the basis to 

 which it is incessantly brought back. 



I will not offer other objections to Mr. Burgess's note, because 

 they would be a repetition of the views enunciated by Dr. van 

 Ermen«em and myself in the paper which the Society has accepted 

 for vol. viii. of the ' Aunales.' 1 will confine myself to pointing out 

 that the uncertainty in which Mr. Burgess finds himself is reflected 

 in the drawing of Coscinodiscus which he publishes, in comparison 

 with that which I have myself given and which he reproduces. His 

 drawinfT shows a line of fracture passing generally above the apertures, 

 and consequently does not allow us to judge of the nature of the 

 latter. Each time, on the contrary, that this fracture passes through 

 an areola, Mr. Burgess draws it clearly open. I have maintained 

 nothinf else. But this figure does not accord with the text, and 

 exactly that which it was necessary to represent is absent in the 

 drawing, that is to say, the form of the membrane which Mr. Burgess 

 supposes to close the apertures of Coscinodiscus Oculus-Iridis and of 

 Trinacria Regina. 



I profit by the opportunity which is offered by Mr. Burgess's note 

 to communicate to the Society, in concert with Dr. van Ermengem, 

 the results obtained by fresh researches on the black opaque matter 

 which covers certain diatoms of the Fiir rock.* These researches 

 complete, in certain respects, our previous observations on this im- 

 portant peculiarity. The first attempts at analysis of the rare 

 specimens which we possessed at that date, had led us to think that 

 this coating was charcoal, arising from a slow combustion of one 

 of the organic layers of the envelope of these diatoms. We 

 Bucceeded in procuring a fragment of the rock in which this substance 

 is more abundant, and, after again making the chemical analysis, we 

 are forced to conclude that, side by side with the carbonaceous 

 masses are found a great nmnber of concretions, and even octahedric 

 crystallizations, formed by pyrites. 



The covering of the valves of Trinacria, amongst others, is due to 

 a deposit of this body. The metallic aspect which it presents, when 

 examined with the Beck reflector, leaves moreover no room for doubt. 

 The presence of this mineral incrustation — distributed sometimes over 

 the whole surface of the valves and faithfully reproducing all their 

 markings, without filling up in any way the lacunce which correspond 

 to the portions taken by the different experimenters for marks in 

 relief or else for depressions — constitutes in our eyes a decisive argu- 

 ment in favour of the thesis which we defend. 



Moreover this pyritization enables us to establish the most interest- 

 in « comparisons with the mineralized diatoms of the London clay. 

 The mode of mineralization of the diatoms of the Fiir rock appears to 

 be the same as that of which the diatoms of the London clay show 

 such remarkable examples, and it seems to us incontestable that these 

 latter are perforated." 



* See this Journal, ante, p. 411. 



