856 Transactions of the Society. 



So much as to methods. The facts in structure of which the 

 photographs are evidence, are these : — 



1. The character of the costse in Navicula major {Pinnularia 



W. Sm.). 



2. The existence of films of silex above and below the large 

 hexagonal cells in Triceratium favus, Coscinodiseus oculus-iridis, 

 and Eeliopelta. 



3. That the " dots " of the diatoms are areolae as shown by the 

 fractured edges of a considerable series of examples, ranging from 

 the coarsest to Pleurosigma angulatum inclusive. 



I do not mean to repeat here the discussion of the subject, but 

 only to present the photographs as illustrative of what I have said 

 in thp series of articles which has been mentioned. 



The Hst of the prints which make up this shorter series of 

 " broken shells " is as follows, viz. 



No. 5. Nitzschia scalaris, and Navicula sculpta Ehr. x 650, 

 exposure 6^ minutes. Fracture through rows of dots between the 

 costse in the Nitzschia, and through the irregular rows nearly 

 parallel to the margin in the Navicula. From MoUer's balsam 

 mount of Sodertelge mud (Sweden). 



No. 6. Epithemia turgida Kiitz. x 760, exposure 6| minutes. 

 Showing sub-rectangular reticulation at broken edge. From same 

 slide as the last. 



No. 7. Navicula lyra Ehr. x 700, exposure 6|- minutes. 

 Showing fracture through radial row of dots between costse, and 

 through the dots on the broken edge. From Holler's balsam mount 

 of Samoa sea-mud. 



No. 10. Navicula maculata Edwards, x 1120, exposure 

 6^ minutes. Similar fracture to the last. From H. L. Smith's 

 mount of Mobile Bay diatoms in dense medium ; ref. index 2 • 4. 



No. 11. Odontodiscus suUilis Ehr. x 1375, exposure 

 10 minutes. Showing wedge-shaped segment broken out, the 

 fracture being through the rows of dots. From Holler's balsam 

 mount of Wedel sea-mud. 



No. 14. Coscinodiseus ohscurus A. Schmidt, x 950, exposure 

 6^ minutes. Showing close hexagonal and loose circular areolation 

 in same shell. From Holler's balsam mount of Nottingham earth. 



No. 17. Same as No. 5. X 960, exposure 6^ minutes. 



No. 20, Odontodiscus subtilis Ehr. x 1320, exposure 

 6^ minutes. Showing a radial crack through a row of dots. From 

 same slide as No. 11. 



No. 21. Coscinodiseus oculus-iridis Ehr. x 1600, exposure 

 9 minutes. Showing dotted film covering the large hexagonal 

 areolsB and projecting beyond the walls of these. From Holler's 

 balsam mount of Nottingham earth. 



No. 22. Same as last, but taken with light a little oblique. 



