Dr. Greville on some British Diatomacese. 261 



have indeed occasionally thought that I perceived a fringe which 

 reminded me of the peristome of some Mosses, but on a closer 

 inspection it disappeared ; and what seemed to be extraordinary, 

 I could not find the spines when I sought for them in the posi- 

 tion most favourable for their exhibition, viz. when viewing the 

 valve vertically or in profile. The point then to be ascertained, 

 seems to be the structure at the boundary line, where the val- 

 vular stria3 terminate at the orifice, and those of the diaphragm 

 commence. And I need not say, that it is with great deference 

 that I venture to take a different view from so high an authority 

 as Professor Smith, and to suggest that the appearance of spines 

 may have been caused by an optical deception. It seems to me, 

 after reiterated examinations with both low and high powers, 

 that the valvular striae simply curve round towards the edge of 

 the orifice to meet those of the diaphragm. The striae (or vittse 

 as they might well be called), being coloured and conspicuous, 

 and the tissue of the valve very pellucid, do present, when 

 viewed in certain lights and in certain directions, the semblance 

 of short processes. In the view I have now given of the struc- 

 ture of the valve at the point of junction, I may however be in 

 error, and I hope that other observers will endeavour to deter- 

 mine the question. The filaments of this species vary in dia- 

 meter from -0007" to -0015". 



EXPLANATION OF PLATE IX. 



Fig. 1 . Eunotia Camelus t The lower figure represents an unusually de- 

 pressed form. 



Fig. 2. Eunotia tridentula. 



Fig. 3. Eunotia quaternaria. 



Fig. 4. Cymbella tequalis. 



Fig. 5. Cymbella lunata. 



Fig. 6. Navicula cocconeiformis. This and all the above as seen under a 

 power of 600 diameters. 



Fig. 7. Portion of a filament of Odontidium anomalum. 



Fig. 8. Three frustules separated, but otherwise in their relative position. 

 Magnified 400 diameters. 



Fig. 9. A single frustule more highly magnified. 



Fig. 10. Frustules of Diatomella Balfouriana ; magnified 400 diameters. 



Fig. 1 1 . A frustule of the average proportion. 



Fig. 12. Frustule in the process of self-division. 



Fig. 13. Side view of frustule. Figs. 1 1-13 as seen under a power of 1000 

 diameters. 



Fig. 14. Portion of filament of Orthosira spinosa; magnified 300 dia- 

 meters. 



Fig. 15. Portion of filament showing the character of the striation, &c. 



Fig. 16. The diaphragm as seen vertically. 



Fig. 17. Orifice of valve with marginal striation, closed by the diaphragm. 



