MaskELL.—On the New Zealand Desmidier. 248 
C. tenue, sp. nov. 
Fig. 10. 
Frond sub-orbicular, the segments slightly broader than long. Ends 
rounded. Edge smooth ; constriction deep, narrow, linear. Frond neither 
punctate nor granulate. A single starch vesicle is visible in the centre of 
each segment. 
End view dlliptio; 
Length of frond 15:5 p; breadth at constriction 8 p 
Not common : my specimens were all found amongst Chara, in running 
water, ncar Christchurch. 
This is a very minute plant, scarcely larger than C. pusillum. It nearly 
resembles C. bioculatum, Brébisson, but differs in the absence of the distinct 
isthmus which, according to Ralfs, connects the segments of that species, 
and in having a deep and narrow, instead of a wide and gaping, constric- 
tion. C. exiguum, Archer (Micr. Journ., 1864, pl. vi.), has oblong seg- 
ments. I find none of the minute Cosmaria described exactly corresponding 
to this form. It has not the colour of C. tinctum, Ralfs. 
5. Xanthidium, Ehrenberg. 
X. cristatum, Brébisson. S. (R. XIX.) 
I have not found this plant in Canterbury. It seems to be not uncom- 
mon in Hawke's Bay. 
X. aculeatum, Ehrenberg. S. (R. XIX.) 
Same remark as for the last species. 
6. Arthrodesmus, Ehrenberg. 
A. incus, Brébisson. S. (BR. XX.) 
Only from Hawke's Day. 
A. convergens, Ehrenberg. 8. (R. XX.) 
Only a single specimen observed, in a gathering from Hawke's Bay. 
The spines on the ends of the segments in this specimen were sigmoid, 
bending slightly outwards. 
7. Staurastrum, Me. 
S. dilatatum, Ehrenberg. (R. XXL.) 
Not uncommon. 
S. alternans, Brébisson. (R. XXI.) 
Rare. 
S. tricorne, Brébisson. S. (R. XXIL.) 
I eannot identify any of my Canterbury specimens with this orm; which 
appears to be common in Hawke's Day. 
Rabenhorst considers the two last as only varieties of S. dilatatum. The 
distinction between S. alternans and S. tricorne is very slight, depending 
upon a ininute prolongation of the angles of the latter into short processes. 
