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A Short Note on Minute Diatom Structure. 

 By Edward M. Nelson, P.R.M.S. 



(Read March 19th, 1897.) 



By the aid of the Powell apochromatic adjustable condenser 

 I am able to report two further results in the resolution of fine 

 diatomic structures. 



The first is the detection of the long-shaped aperture in the 

 nodule of Xavicula rhomboides. A figure is unnecessary, because 

 it is a minute edition of the structure beautifully drawn by 

 Mr. Karop in our journal at Fig. 19, PI. XX., Yol. 4, Ser. II. 

 The pipes and the central spot in the nodule were of course 

 familiar, but the aperture in the centre had not been seen 

 before in so small a navicida. The whole spot in the nodule in 

 N. rhomboides is not so large as the aperture in Fig. 19, and it 

 was in this minute structure that the still smaller aperture was 

 seen. It was not merely glimpsed, but it was well seen on this 

 occasion, and irregularities in the aperture similar to those in 

 Fig. 19 could be perceived. 



The second structure relates to a diatom Biddidphia elaborata 

 (Gr. and St.) mounted in styrax. The termination of the stalk 

 of this diatom, which is known as the rose of the diatomic 

 watering-pot, was figured by Mr. Karop in our journal at Fig. 5, 

 PI. IV., Yol. 3, Ser. II. The diatom itself is figured by Messrs. 

 Grove and Sturt, at Fig. 9, PI. XVIII., Yol. 2, Ser. II. That 

 drawing, however, does not show the rim which is attached to 

 the oval periphery of the valve, and which is -00041 inch high. 

 The general appearance of the valve might aptly be compared to 

 an oval tea tray, having a convex mound in the centre as high 

 as the rim, and a pipe, with a watering-pot rose top, rising 

 up a little distance from the ends of its longer axis. The 

 " close set papillse," which are small pipes probably analogous 

 to the perforation in the nodule in a navicula, rise from the 

 centre of a crater which is at the top of an elevation in the 

 middle of the valve. The edge of the crater is approximately 

 level with the top of the rim round the periphery of the valve. 



Journ. Q. M. C, Series II., No. 41. 30 



