Maskell. — Oil Neto Zealmul Desmidieae. 21 



the centre of each segment. In the present plant this projec- 

 tion is so shght, so round, and so free from granules that the 

 generic position of the plant is not easily fixed. In a general 

 way it belongs probably to the series of X. aculeatinn, Ehren- 

 berg, but it is not that species. It is smaller than X. 

 octonarium, Nordstedt (also a New Zealand plant), and has 

 many more spines. Hereafter it may be found necessary to 

 relegate it to the genus Cosmarium, but even then it will have 

 to occupy a rather doubtful position, something like INIoham- 

 med's coffin. 



Genus Arthrodssmus, Ehrenberg. 



Arthrodasmus convergeiis, Ehrenb., var. divaricatus, var. 

 nov. Plate IV., fig. 34. 



Frond resembling generally the original type, with the 

 segments in front-view elliptical, though the edges are usually 

 very slightly angular (so slightly as not to form a distinctive 

 character). The spines converge at first and then diverge in 

 a regular curve, and they are blunt, if not even a little dilated, 

 at the tip. In end-view the spines are straight. 



Long., 36 /x ; lat., 33-5 /x ; crass., 13 /x ; long, spin., 8 /x. 



Hawke's Bay ; Otaki. 



I mentioned" this plant in my paper of 1882 ("Trans.," vol. 

 XV., p. 243), but, as I had at that time only seen one specimen, 

 did not think it desirable to found a variety on it. Since then, 

 however, I have obtained a number of specimens, all agreeing 

 in the above characters, and venture therefore to consider 

 them as not exactly conforming to the type. I have seen two 

 or three specimens of larger size, reaching long. 56 /x, lat. 

 45 fx. 



Arthrodcsuuis incus, Brebisson. 



Besides the forms a, c, d of Ealfs ("Brit. Desm.," pi. xx.), 

 reported by Professor Nordstedt (" N.Z. Alg.," p. 45), I have 

 specimens of the form b from Otaki. The plant is very 

 variable in shape, and seemingly also in size. 



Genus Staurastrum, Meyen. 



Staurastrum dilatatum, Ehrenberg, forma. Plate IV., 

 fig. 35. 



Frond small ; constriction deep and wide ; segments in 

 front- view elliptical, in end-view triangular, with slightly con- 

 cave sides and widely-rounded angles ; cytioderm punctate. 



Long., 30-35 /x : lat., 34-41 /x. 



Christchurch ; Hawke's Bay ; Otaki ; Wellington. 



Professor Nordstedt reports a form, S. dilatatum, var. 

 ohtusilohum, De Notaris, from New Zealand, but with four- 

 angled end-view. All the specimens I have observed have but 

 three angles. 



