636 PLANKTON OF THE SYDNEY WATER-SUPPLY, 



Var. DETUITA, n.var. (Pl.lvi., f.23). 



Frustula angusta, linearis, leviter sigmoidea; lateribus parallelis; 

 apicibus rotundatis. 



Long. 40-60; lat. 5 fi. 



This form develops into the slender form of var. Herihaudii, 

 f.21, by growth at the apices, the frustule thus becoming more 

 sigmoid, and the apices produced and pointed. They both are 

 very common in the waters round Sydney, being always found 

 associated together, with the type more sparsely intermixed. 



Genus Melosira Ag. 



MeLOSIRA GRANULATA(Ehr.) Ralfs. 



Diam. fil. 3^, 4, 6, 8, 10, 12, 15, 20; cell. alt. 30, 34, 25, 20-27, 25, 

 20,20-24, 16-20/^. 



In prodigious quantities, absolutely swamping everything else. 

 The filaments of diam. 20 /i (relatively few) had granules very 

 distinct, arranged squarely in 13 longitudinal and 7 transverse 

 rows. Some filaments were observed deeply rufescent, and, in a 

 few, the cytoplasm, instead of being yellowish, was of a bright 

 strong green colour. 



Var. ciRCiNALis, n.var. 

 The filaments curved into a perfect circle, or arc of a circle. 



Genus Cyclotella Kiitz. 

 Cycl. Meneghiniana Kiitz. 

 Diam. 10, 12, 14, 15, 16, 18, 20, 22/i. 



Var. MiNUTissiMA, n.var, (PI. Ivi., f.24). 

 Diam. 4, 5, 6, 8, 10/x. No.90. 



No markings or striae whatever, save that, on the largest, a 

 rosette of dots appears in the centre, representing the areolae of 

 var. stelligera. The striae, however, will appear with growth. A 

 good proof that these frustules are all in a state of growth, is 

 found, it seems to me, in the fact that it is quite easy to obtain 

 an ascending series of sizes connecting the smallest with the 



