254 
W. J. Hodgetts. 
NOTES ON FRESHWATER ALG^E. I —IV. 
By W. J. Hodgetts, M.Sc. (Lond.) 
[With Two Figures in the Text.] 
I.—A New Species of Pyraminionas. 
D URING April and May, 1920, a small motile Alga belonging to 
the genus Pyramimonas (family Polyblepharidacese of the 
order Volvocales) was observed in fair quantity among filaments of 
Spirogyra and Tribonema in the overflow ditch of a small pond at 
Quinton, near Birmingham. The Alga appeared to be absent from 
the pond itself, occurring only in the very shallow water of the ditch, 
into which, owing to the heavy rains of April, water from the pond 
had run. The water of the ditch in places was coloured light green 
owing to the presence of this Alga. On keeping specimens in the 
laboratory in open tubes and wide-mouthed glass jars the organism 
always became encysted after 24-36 hours, and eventually died; 
and attempts to cultivate it in dilute nutrient solutions were also 
unsuccessful. 
The form of the motile cell is very variable, the commonest 
shape being sub-pyramidal (Fig. 1, A), sharply truncate and slightly 
4-lobed at the anterior end, and somewhat tapering towards the 
posterior extremity. Transitions to shorter forms which are more 
or less cordate (Fig. 1, B), or even sub-globose were frequent; while 
on the other hand more elongated sub-cylindrical individuals (Fig. 
1, C) were not rare. The widely truncate anterior end is a character¬ 
istic feature of all the cells, and when the latter are observed in 
anterior view this end is sub-quadrate with rounded angles (Fig. 1, 
D), due to the four anterior lobes. The usual number of these 
lobes was four, but occasionally only three were seen in anterior 
view, giving a sub-triangular form to this end of the cell. The 
anterior lobes are strictly confined to the anterior end of the cell, 
and are not continued backwards as ridges, or at any rate are 
continued for only a very short distance, so that the (optical) 
transverse section for the greater part of the length of the cell is 
circular. There is a well-marked depression in the centre of the 
anterior end, and from the base of this depression arise four cilia. 
The motion of the cell is always cilia-end foremost, while at 
the same time the cell rotates about its longitudinal axis in a 
direction which (the cell being considered as swimming towards the 
observer) is clockwise. 
