THE YAN YEAN RESERVOIR, VICTORIA. 19 
Lagerstedt’s Spitsbergen specimens of Navicula bicapitata, but are distinctly 
produced and slightly dilated. There is a clear space of considerable width 
on each side of the raphe, owing to the shortness of the strive, and in the 
middle opposite the central nodule this clear area widens still further. The 
striæ do not cease, however, in the median part of the valve ; they strongly 
converge towards both the central and terminal nodules, and are about 9—10 
in 10 д. 
In outline this form agrees fairly closely with Pinnularia microstauron, 
Cleve, Synops. Navie. Diat. ii. 1895, p. 77 (= N. bicapitata var. hybrida, 
Grun. ; ef. Van Heurck, Le. t. 6. fig. 9), but the stri: do not cease in the 
middle. It is also very near Navicula subcapitata, Greg., especially in the 
less capitate poles, but as the striæ do not stop on each side of the middle, 
and the poles are distinctly angular, I have regarded it as more nearly 
approaching N. eapitata. In outline it bears much resemblance to 
N. kefringensis, Ehrenb., from Jaaling, figured in Schmidt’s Atlas Diat. t. 47. 
fig. 63, but the extremities are not quite so narrowed and the striæ do not 
reach so close to the raphe. 
Perhaps the form seen so abundantly from Australia should be regarded as 
Pinnularia microstauron, (Ehrenb.) Cleve, but it seems almost impossible to 
demarcate between P. interrupta, P. mesolepta, P. microstauron, №. bicapitata, 
and V. subcapitata, as their numerous forms constitute a continuous series. 
The Australian forms agree more closely with the published figures of 
N. bicapitata than with any other, and I have for the present adopted that 
name. 
Genus GYROSIGMA, Hass. 
65. GYROSIGMA ELONGATUM, ( W. Sm.) nob., var. ? 
Long. 362 ш; lat. med. 22 и. (РІ. 3. fig. 17.) 
Hab. Yan Yean Reservoir, very scarce in the plankton (Nov. 1905). 
This Gyrosigma differs very much from any other species I have observed 
in fresh water, and I can find no figure exactly corresponding to it in 
Peragallo’s * Monogr. Gen. Pleurosigma, Le Diatomiste (1890-91). The 
nearest are * P. decorum, W. Bm., var. ? americanum, Рег.” (== P. longum 
Cleve, var. americanum (Per.), Cleve), and P. elongatum, W. Sm. (vide 
Peragallo, l.e. р. 5, t. 1. fig. 9, and p. 7, t. 3. fig. 5). The first of these is 
perhaps the nearest as regards outline and the position of the raphe, but the 
striæ are very delicate and oblique as in P. elongatum. The extremities of 
the valves are about as acute as those of P. elongatum (especially Peragallo's 
fig. 8 on t. 3), but the raphe is very decidedly oblique and not central. The 
Australian plant has also a more elongate median part of the valve, in which 
the margins are parallel for some distance, and the central nodule is likewise 
oblong-elliptic. 
