Wills, A. W. On the Desmidieæ of North Wales (in “Midland Naturalist”). 1881. Wolle, F. Desmids of the United States. 1884. —— Fresh-water Algæ of the United States. 1887. Also detached papers on Desmidieæ and other Algæ by Nordstedt, Wittrock, Marquand, and others. Professor Nordstedt's paper on the New Zealand Algæ, included in the above list, is specially valuable. It contains descriptions, with seven plates, of about one hundred and fifty species and varieties of Desmidieæ. I have to make the following remarks and corrections regarding some of the plants included in my two former papers. These are rendered necessary by more accurate knowledge acquired since 1882, either by observation, or by more extended access to the literature of the subject, or by suggestions from Professor Nordstedt, Mr. Turner, and others. Aptogonum undulatum (“Trans. N.Z. Inst.,” vol. xiii.). The genus Aptogonum is now by most writers considered as properly only equivalent to Desmidium, Agardh; and Professor Nordstedt attaches my plant as a variety to D. baileyi, de Bary. In his description and figures (“Alg. of N.Z.,” p. 27, and pl. ii., 8) he does not, I think, express altogether the convex curve of the upper portion of each cell as seen in front-view (or, as I called it in 1880, the “side-view,” meaning as in filament). His specimens appear to be more angular than any I have seen, and I have re-examined for comparison a number of preserved specimens and a few fresh ones. Also, he states that in all cases the end-view is “regularly triangular, with rounded angles and almost straight sides. “I find that this is so as a rule; but several specimens exhibit an end-view similar to that given in my paper of 1880 (vol. xiii., pl. xi.), except that the printers then added a sort of loop or curved open ring, which was not in my original drawing, and instead of which there should have been only the three small processes near the angles. Micrasterias rotata (vols. xiii. and xv.). This, which I reported with very great doubt in 1880 and 1882, turns out to be M. schweinfurthii, Cohn, a Central African plant. My fig. 16b (vol. xv.) is a form of M. angulosa, Hantzsch. Euastrum binale, forma (vol. xiii.). The fig. 26 in pl. xii. is the variety denticulatum, Kirchner. See the present paper, with more accurate figure. (Pl. II., fig. 12.) Holocystis incisa (vol. xiii.). This is Micrasterias decemdentata, Naegeli, var. upsaliensis, Cleve. Cosmarium ralfsii (vol. xiii.). This is very near to C. pseudopachydermum, Nordstedt (“N.Z. Alg.,” p. 53), and is not