On some Peculiar Forms of Navicula from the Sulu Archipelago

Abstract

ABSTRACT Great diversity of opinion has existed among the most distinguished writers on the subject of the Diatomaceæ, as to the question whether Ehrenberg’s separation of Pinnularia from Navicula is tenable or not. The ground on which this distinction is made rests on the character of the striæ, which in Pinnularia are supposed to be costate, while in Navicula they are moniliform. Kützing rejected this distinction, while W. Smith and Rabenhorst maintained its validity. Ralfs in ‘Pritchard,’ p. 892, included the forms of Pinnularia under the genus Navicula, and gives his reasons for adopting this course as follows:—”Were the costæ always plainly developed, as in Pinnularia nobils and its allies, no difficulty could occur in determining the genera, but in many of the more minute species it is often very difficult to distinguish between striæ and costæ. We have not admitted Pinnularia here, partly for the reason just given, but principally because we cannot decide to which genus a large number of Ehrenberg’s species should be referred.” The existence of the distinctive characteristic is here admitted, but the genus founded on it rejected on account of the difficulty of applying it in many cases.