The following list of the works on the Desmidieæ which are now (1888) available to me here is given as a guide to anybody desiring to further investigate the family in New Zealand. They do not form more than a small portion of the whole bibliography of the subject, but are sufficiently comprehensive for most purposes. However, every year is adding to the number of works on Desmids.

• De Bary, A. Untersuchungen über die Familie der Conjugaten. 1858.

• Bennett, Dr. Fresh-water Algæ of the English Lake District (in “Journ. of Roy. Micros. Soc.”). 1886.

• Bisset, J. P. List of Desmidieæ found in the Neighbourhood of Lake Windermere (in “Journ. of Roy. Micros. Soc.”). 1884.

• Delponte, J. B. Specimen Desmidiacearum subalpinarum. 1873.

• Ehrenberg, C. G. Die Infusionsthierchen. 1838.

• Joshua, W. Burmese Desmidieæ (in “Linn. Soc. Journ.”). 1886.

• Lagerheim, G. Contributions Algologiques à la Flore de la Suède. 1886.

• —— Bidrag till Amerikas Desmidié-Flora. 1885.

• —— Ueber einige Algen aus Cuba, Jamaica, und Puerto-Rico. 1887.

• —— Ueber Desmidiaceen aus Bengalen. 1887.

• —— Sopra Alcune Alghe d'acqua dolce. 1888.

• Lundell, P. M. De Desmidiaceis quæ in Suecia inventæ sunt. 1871

• Maskell, W. M. Contributions towards a List of the New Zealand Desmidieæ (“Trans. N.Z. Inst.”). 1880.

• —— Additions to above Catalogue (“Trans. N.Z. Inst.”). 1882.

• —— On a New Variety of Desmid (“Trans. N.Z. Inst.”). 1885.

• —— Note on Micrasterias americana, Ralfs, and its Varieties (in “Journ. of Roy. Micros. Soc.”). 1887.

• Nordstedt, O. Symbolæ ad Floram Brasiliæ centralis cognoscendam—Desmidiaceæ. 1869.

• —— Desmidieæ ex insulis Spetsbergensis et Beeren Eiland. 1872.

• —— Bidrag till Kännedomen om sydligare Norges Desmideer. 1873.

• —— Desmidieæ arctoæ. 1875.

• —— Desmidieæ et ædogoniæ in Italia et Tyrolia collectæ. 1876.

• —— Nonnullæ Algæ aquæ dulcis Brasilienses. 1877.

• —— De Algis aquæ dulcis ex insulis Sandvicensibus. 1878.

• —— De Algis nonnullis, præcipue Desmidieis, inter Utricularias Musei Lugduno-Batavi. 1880.

• —— Desmidieer samlade af Sv. Berggren under Nordenskioldska expeditionen till Grönland. 1885.

• —— Fresh-water Algæ collected by Dr. S. Berggren in New Zealand and Australia. 1887.

• Pritchard, A. Infusoria (Desmidieæ by W. Archer). 1861.

• Rabenhorst, L. Flora Europæa Algarum aquæ dulcis et submarinæ. 1868.

• Ralfs, J. The British Desmidieæ. 1848.

• Roy, J., and Bisset, J. P. Note on Japanese Desmids (in “Journ. of Botany,” July and August). 1886.

• Spencer, Dr. Notes on Fresh-water Algæ (“Trans. N.Z. Inst.”). 1881.

• —— Continuation of the above. 1882.

• Turner, W. B. Notes on Fresh-water Algæ (in the “Naturalist”). 1886.

• —— On some New and Rare Desmids (“Journ. of Roy. Micros. Soc.”). 1885.

• Wallich, Dr. Descriptions of Desmidiaceæ from Lower Bengal (in “Annals and Mag. of Nat. History”). 1860.

• 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

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.

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.

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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