connatum, Lundell. Nordstedt observes that the spines in his specimens do not diverge as much as shown in my figures. I have since re-examined my specimens, and find that in the majority the spines, if produced inwards, would meet exactly at the middle of the isthmus, as in my pl. xxiv., fig. 12a: a few of them are less divergent, as in my fig. 12b. Docidium dilatatum (vol. xiii.) is D. ovatum, Nordst. (“Desm. Brasil.”), now attached to the sub-genus Pleurotanium. The measurement given in my paper of 1880, “length, 1/33in.,” is a clerical error; it should have been “1/66in.” Triploceras tridentatum (vol. xiii.); the same, var. cylindricum (vol. xv.); the same, var. superbum (vol. xviii.). The distinctions upon which I based this new species and its variations, as separating it from T. verticillatum and T. gracile, Bailey, from T. pristidæ, Hobson, and T. gracile, Archer, were the presence of three denticulatious on the terminal processes and two tricuspidate projections just below them. Professor Nordstedt considers the last as accidental. On re-examining my specimens of var. cylindricum I find that some have the projections, others have not; consequently these cannot be used as sufficient distinction. Nordstedt attaches my var. superbum to T. verticillatum, and my var. cylindricum to T. gracile, Bailey; but he says that in neither has he been able to see the terminal processes tridentate. In all of the eighteen specimens I have preserved of both, the three teeth are very distinct and clear, although in some which are slightly turned towards the eye the third tooth is seen only foreshortened. There is indeed a marked difference between these two plants and T. aculeatum or T. bidentatum, Nordst. (“N.Z. Alg.,” p. 64), of which I have also specimens. In these last the terminal teeth are never, as far as I have seen, more than two, and sometimes only one is visible. Of the original T. tridentatum I have unfortunately no specimens now, and the locality where it was gathered is no longer available. It will be worth while for some one to make a thorough examination of the plants of this genus in New Zealand, for they are very beautiful and worthy of full investigation. On the whole, I venture to maintain my original diagnosis; and, if T. verticillatum and T. gracile never have three terminal denticulations, I think my plants are rightly separated from both. The localities in New Zealand where Dr. Berggren collected Algæ appear to have been very numerous, ranging from the Bluff to the Bay of Islands. I do not see, however, in the list given in Professor Nordstedt's paper any places in Hawke's Bay or on the south-western coast of the North Island. Most of the new species and varieties mentioned in this present paper and former papers of mine have been collected in these