BIOLOGICAL STUDY OF TAP WATER. 417 
considerably, being more or less lunately curved, semi-circular, bent 
into a loose spiral, or sometimes resembling very much a pair of 
cow’s horns; extremities greatly attenuated. On one or two occasions 
a larger form was observed, which agreed very closely in characters 
with these smaller ones. The frond was lunately curved, varying to 
sigmoid or spiral ; distance between the extremities about 30 times 
the breadth; upper margin very convex, lower very concave ; no 
central inflation ; tapering gradually to an acute point at the 
extremities ; contents granular. Diam. 0:0038 mm. ( = 0:000155”). 
Habitat, Lake Ontario, Fig. 2. 
In one gathering a fine living specimen was noticed which in 
most of its characters seemed to approach more nearly to Clos. 
parvulum, Naegl., than any other, though in some respects it resem- 
bled Clos. Venus as described by Wood. In size however it differed 
from both of these. The diameter was found to be 0-0186 mm. 
( = 000074"), and the length about 8 times as much. The measure- 
ments given by Rabenhorst for Clos. parvulum are diam. max. 
0-00026”—0-00062”", and length 6-8 times as much ; and according 
to Wood the diameter of forms referred by him to this species is 
00008”. Clos. Venus has a diameter of 0:0004”, and is 8-12 times 
longer than broad. The general appearance of the form was very 
similar to that of Clos. parvulum as figured by Wood, and as the 
actual size of any species can hardly be regarded as fixed within 
narrow limits, it has been referred to Clos. parvulum. 
Another interesting form which is nearly always present approaches 
in some respects the description of Clos. setacewm, but is not accurately 
described in any work at my command; accordingly I propose for 
it the name Clos. filiforme, with specific characters as follows :— 
Closterium filiforme, n. sp. Frond very slender, greatly elongated, 
15 
each extremity being a colourless beak as long, or nearly as long, as 
the body ; filiform, cylindrical, smooth, not lunately curved, belly 
not inflated, gradually attenuated towards the apices, which are 
rounded and slightly curved downwards ; vacuoles 3-8 in each limb 
in a single series. Breadth 0.0062 mm- ( = 0:00025”"), length 
0:-4154 mm.—0-62 mm. ( = 0:0166”—0-025”), or say 60-100 times 
the breadth. Habitat, Lake Ontario, Fig. 3. 
Clos. Griffithsii has also been observed. Other Desmids were 
Staurastrum gracile, Stawr. punctulatum, and a species of Cosmariwmy 
probably Cos. cucwmis. 
