THE 



MONTHLY MICROSCOPICAL JOURNAL. 



MAY 1, 1876. 



I. — Note on the Markings of Navicula Rhomhoides. 



By Dr. J. J. Woodwakd, U. S. Army. 



{Read he/ore the Royal Microscopical Society, April 5, 1876.) 



Plates CXXXV. and CXXXVI. 



Mr. Hickie's reply to my " Note on the Markings of FrustuUa 

 Saxonica " * was unfortunately crowded out of the February num- 

 ber of the Journal, and I will therefore postpone any discussion of 

 the views I am informed he has expressed until I see his paper. I 

 have, however, received through the politeness of Mr. John Mayall, 

 jun., copies of Herr Seibert's photographs, which Mr. Hickie 

 exhibited as photographs of FrustuUa Saxonica at the meeting of 

 the Koyal Microscopical Society, January 5, 1876, and I desire to 

 offer a few remarks with regard to them. 



In the fii'st place, I must compliment Herr Seibert on his suc- 

 cess in photographing what he saw ; and his willingness to exhibit 

 the photographs is a proof of his sincerity. Next, I desire to point 

 out the convenience and accuracy of photography for the purpose 

 of such a discussion as this. Without it I should have been unable 

 to form any definite opinion as to what Herr Seibert had seen. 

 Lastly, I must express my conviction that the remark attributed to 

 Mr. Mayall in the report of the proceedings of the meeting men- 

 tioned,! that the diatom photographed by Herr Seibert was " a 

 coarse form of Khomboides," is quite correct. 



This conviction is forced upon me by a consideration of the dis- 

 tance of the striae apart, in connection with the size and shape of 

 the diatom as shown in Herr Seibert's photographs. These make 

 the diatom four inches long. The length of FrustuUa Saxonica 

 varies from -0012 to -0030 of an inch. (On a slide labelled 

 FrustuUa Saxonica, loaned by Mr. Hickie to Mr. Mayall as 

 authentic — to which I assented — and loaned by Mr. Mayall to me, 

 I found none any longer than • 003 of an inch.) If, then, Herr 

 Seibert has photographed even the coarsest of these forms, his 

 pictures are taken with over thirteen hundred and thirty diameters. 

 But his photograph of the transverse markings gives 110 lines to 



* ' Monthly Microscopical Jouriifxl,' Dec. 187o, p. 274. 

 t Ibid., Feb. 187G. p. 103. 

 VOL. XV. 



