the species to which I first referred it. Nordstedt's specimens, most of which seem to have come from the Canterbury District, as mine did, had not the deep incrassation at the ends shown in my pl. xii., fig. 30 (1880). I have re-examined my specimens, and find the incrassation very distinct in most of them, though some are without it. Cosmarium crenatum (vol. xiii.). This is C. naegelianum, Brébisson, var. latum of my present paper. C. undulatum (vol. xiii.). is C. speciosum, Lundell. Vide post. C. undulatum, var. β (vol. xv.), appears to me now to be somewhat near C. impressulum, Elfving, as figured by Roy and Bisset (“Japan Desm.”); but I have not specimens at hand for comparison. C. margaritiferum (vol. xiii.). The three forms figured by me in 1880 appear to belong to different species. Fig. 27 is probably C. sublatum, Nordst.; fig. 28, C. quaternarium, Nordst.; and fig. 29, C. reniforme, Archer, which is at least very closely allied to C. margaritiferum. C. broomeii (vol. xiii.). This is C. sublatum, Nordst.; but I am not able to see the difference between this new species and Lundell's C. latum. C. thwaitesii (?) (vol. xv.) is Penium cucurbitinum, var. subpolymorphum, Nordst. C. gemmiferum (vol. xv.) is C. magnificum, sp. nov., Nordst. C. speciosum, var. inflatum (vol. xv.). Professor Nordstedt makes this C. subspeciosum, var. validius, var. nov. In accepting the correction, I cannot help remarking that the differences between C. speciosum and C. subspeciosum do not appear to be very important. C. cyclicum, var. ampliatum (vol. xv.). In accordance with a suggestion from Professor Nordstedt, I describe and figure this in the present paper as C. subcyclicum, sp. nov. C. tetraophthalmum β minus (vol. xv.) is C. subpunctulatum, Nordst. Staurastrum avicula (vol. xiii.) is S. subdenticulatum, Nordst. Staur. (Didymocladon) stella (vols. xiii. and xv.) are forms of S. sexangulare, Bulnheim. Staur. aculeatum (vol. xv.) is S. splendidum of the present paper. Staur. clepsydra (vol. xii.). This name having been previously taken, Professor Nordstedt, at my suggestion, altered it to S. spencerianum. He considers the plant a variety of S.