The author stated that he had examined, more or less minutely, nearly 300 fresh-water gatherings, and that he had found in these very nearly all the known British species, besides a number not yet described. He mentioned that, from the want of figures, it was often difficult to know whether a form were new or not. Thus, Pinnularia latestriata, found by the author two years since in the Mull earth, had been considered as a new species by all British naturalists, as well as several foreign ones; yet in Ehrenberg's last work, “Mikrogeologie” it is figured as P. borealis, and as having been described by Ehrenberg ten or twelve years ago. The papers of that author, in the Berlin Reports and Transactions, are not generally accessible.