Page:Transactions NZ Institute Volume 15.djvu/330

S. punctulatum, Brébisson. (R. XXII.)

Common.

Distinguishable from S. dilatatum chiefly by the more turgid segments and generally rougher frond.

S. aculeatum, Ehrenberg. (R. XXIII.)

Not common: as yet only from the Bryndwr ditch. It is curious that this ditch, perhaps twenty yards long, a couple of feet wide, and a few inches in depth, should have contained so many species of Desmidieæ, most of them too of great interest and beauty.

S. spinosum, Brébisson. (R. XXII.)

Very rare: indeed I am not sure that this plant occurs here. Rabenhorst makes it only a variety of S. (Xanthidium) furcatum, Ehr., a plant which Ralfs mentions only doubtfully.

Some specimens in gatherings from Hawke's Bay were referred by Dr. Spencer to this species, but on close examination appear to me to be rather the next.

S. eustephanum, Ehrenberg, var. emarginatum, var. nov.

Frond in side view deeply constricted at the middle: the constriction wide, gaping. Segments sub-elliptic, the lateral margins convex or turgid, the outer margins nearly straight, sometimes concave. At each angle appear three spines, not in the same plane: the terminal spine long, subulate, tipped with a sharp awn, the two others shorter, cylindrical, forked at the tip. These processes are quite smooth, but I think there is sometimes a minute punctation on the frond. In an empty frond the terminal processes of the third angle can be seen foreshortened on the segments. There are no processes on the edges, except at the angles.

Frond in end view triangular, the sides of the triangle emarginate, or widely crenate, being a little inflated at the middle. Each angle terminates in a somewhat elongated cylindrical or subulate process tipped with a sharp awn. On the sides, close to the angles, are seen six other processes, shorter than the terminal ones, cylindrical, and forked at the tip, and the bases of these are conjoined; they are not on the plane of the triangle, so that they present somewhat the appearance of a star with six short rays. At the base of the fork, on each process, there is an exceedingly minute spine. The processes are smooth and project a little beyond the sides of the triangle, not perpendicularly to the sides but pointing somewhat towards the angles.

The whole plant is very minute; average length of segments in side view (exclusive of processes) 23μ: length of side of triangle in end view (exclusive of awns) 25μ; length of awns 4μ.