516 PLANKTON OF THE SYDNEY WATER-SUPPLY, 



Dinohryon above cited, with a single variable organism, 

 whose extremes of variation only have been regarded as sepa- 

 rate species. The connecting links are sufficiently abundant 

 still, and the union of several types in a single colony is 

 sufficiently frequent to lend some weight to my conclusions 

 with regard to those forms which have been under my obser- 

 vation." The italics are Prof. Kofoid's. My own observa- 

 tions abundantly indicate that this is applicable to all aqua- 

 tic micro-organisms both vegetable and animal. A very 

 common rule is that the genus and the species are one, the 

 accepted "species" being merely forms brought about by 

 varying modes of growth. D. serfiiJarid var. cylindriciim 

 (Imhof), D. sertularia var. divergens (Imhof), and D. sertu- 

 Jarin var. Schauinslandii (Lemm.) are found in the Sydney 

 Water-Supply (Plate Ivii., figs. 6-8). 



CHLOROPHYCE^. 



Genus Pediastrum Meyen. 



Pediastrum tetras var. longicornutum (Rac). Nonn. 

 alg. nov., T.vii., f.64. 



Diam., c.proc. 15; s. proc. 9/u,. 



In company with {Grncigenia) tetrapedin. This form is a 

 variant of Ped'i. tetras var. Ehrenhergii. As found in the 

 plankton, it was plainly the outgrowth of (Crugigenia) tetra- 

 pedia (Kirchn.) W. & G. S. West, which accompanied it. 

 (Pl.lvi., f.l. Compare PI. Ivi., f.8,9, for a similar growth). 



Var. australe, n.var. (Plate Ivi., f.2). 



Coenobium crucigeniseforme, in medio foramine instructum ; 

 cellulis 4, subtriangularibus ; angulis exterioribus subaoutis ; 

 margine exteriori medium leviter inflate. 



Long. 10, lat.8/x. 



The lower cell of the four has not developed pari passu with 

 the others. Compare W. & G. S. West, Alg. N. Ire., Pl.i., 

 f. 11-12, out of which our form develops. 



