Maskell. — On New Zealand Desmidiese. 311 



This fine plant appears to be most nearly allied to D. truncation, Bre- 

 bisson, but it differs from that (and, indeed, I think all the other species 

 of Docidium) in the total absence of all inflations at the base of the 

 segments. The edge of D. dilatatuvi is continuously smooth from the 

 median suture to the terminal angles, whereas even in D. truncatum. (where 

 the inflations seem to be smallest) there is apparent a slight undulation of 

 outline. It difi'ers also from D. truncatum in the presence of the terminal 

 tubercles, absent in that species. Moreover, the bold dilation of the 

 segments near the base, the subsequent tapering, and again subsequent 

 dilation to the end, seem to distinguish the plant from all others of the 

 genus. D. coronatum, Brebisson, has similar terminal tubercles, but 

 otherwise is quite different. 



12. Triploceras, Bailey. 



A genus separated from Docidium on account of the projecting pro- 

 cesses at the ends of the segments. In the American, Indian, and Chinese 

 species these seem to be indifferently set down as being two or three. The 

 generic name implies three ; my species has two. 



T. tridentatum, sp. nov. 



Figs. 21-23. 



Frond small, slender, depressed, very slightly constricted at the middle. 

 Total length, about twelve times the breadth in front view. 



Segments furnished with a number (fifteen to eighteen) of whorls of denti- 

 culate projections pointing generally towards the extremity, but those near 

 the middle of the frond project more perpendicularly. Edges between the 

 teeth linear, not curved. Between the last whorl and the terminal projec- 

 tions is a short space without whorls, and at the base of the terminal 

 processes are (at each side) three angular tri-cuspidate smaller processes 

 (fig. 23). 



Terminal processes two, sub-rectangular, divergent, ending each in three 

 sharp teeth. Edge of frond between the processes curved. 



Lateral denticulations not conical, but somewhat quadrate, like the 

 teeth of a circular saw, pointing forwards. 



Endochrome dark green, darkest at the axis. At the middle is a small 

 lighter green space, in which often granules may be seen "circulating," 

 that is, travelling in distinct currents — those near the axis from the ex- 

 tremity of the frond to the middle, those near the edge from the middle 

 towards the extremity of the frond. 



The section is rectangular, and in side view the frond is much narrower 

 than in front view. 



I think the empty frond is punctate, but the puncta are extremely 

 minute and require a high power to distinguish them. 



