On the Markings of Diatomaceæ

Abstract

ABSTRACT It is not easy to over-estimate the importance of the department “Notes and Correspondence” in your Journal. Not only does it afford a means of recording facts which might otherwise remain unpublished; but the various hints and memoranda contained in it possess a value to the country student which those only who are similarly situated can appreciate. The note by Dr. Greville, “On a Structure observed in Surirella,’ vol. vii, p. 116, recalled my attention to the subject of the present article, and reminded me that on two occasions I had observed something similar in naviculoid frustules. The first was in Pleurosigma balticum, where the internal marking was hexagonal; and the second in a frustule of Amphipleura pellucida, where there were transverse lines, but much more distant than the 130 to 001” observed in that species by the Hull microscopists. Ill neither of these instances were the slides my own, and they were not seen under circumstances which enabled me to do more than record the fact of their occurrence. In neither case was the idea of a septum entertained; the internal markings had distinctly the curve of the side of the frustule, and the impression conveyed was simply that both surfaces of the silica were marked. I had the less hesitation in coming to this conclusion, from having frequently seen something similar, but apparently constant, in certain disciform species. The fact that certain species of Actinocyclus, &c., have two very evident sets of markings is generally known. It is hardly less probable that the same thing has been seen in Coscinodiscus centralis, and that the fine secondary markings of Triceratium favus (indicated by Dr. Wallich in what he calls T. fimbriatum) have been observed by those who have directed their attention to that species.*