BIOLOGICAL STUDY OF TAP WATER. 417 



considerably, being more or less Innately curved, semi- circular, bent 

 into a loose spiral, or sometimes resembling very much a pair of 

 cow's horns; extremities greatlv 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 charactei*s 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. 

 ( = 0*00074"), 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 

 0*0008". 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. setaceum, 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, 

 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. Grijfithsii has also been observed. Other Desmids were 

 Staurastrum f/racile, Staur. punctulatum, and a species of Gomxa/riwnw 

 probably Cos. cucumis. 



