BY G. 1. PLAYFAIR. 519 



Cf. Bohlin, Erst. Regnellsch. Exp., T. i., f. •Jl-22. Bernard, 

 Protococc. et Desm., PI. xii., f.390. Nageli, Gatt. Einz. Alg., 

 T. iii., fig.C n. 



All the forms of Nephrocytium belong to the one species, N. 

 Ayardhianum Nag. 



Var. LUNATUM(West) Chod. 

 Forma cellulis paullo crassioribiis. 

 Cell. long. 18-21, lat. 7-8 /x. 



Genus Tetrakdkon Kiitz. 



Tkth. lobulatum var. SYDNEYENSE(Playf.). 



Syn., Stauropha7ium cruciatum (3 elegans f. Sydneyensis, antea 

 1907, PL v., f.30. 



Var. UECUSSATUM(Reinsch) mihi, forma. (PI. Ivi., f.lO). 



Forma corpore profunde inciso cruciforme; brachiis angustis 

 lateribus psene parallelis, processibus plus minus frondescentibus 

 instructis. 



In tliis form, the two opposite ai-ms are bent upwards, and the 

 other two downwards; indicating the transition in growth from 

 the flat shape to the tetrahedral. I have noted the same in 

 Tetr.ininimuni. Reinsch's Folyedrium decussatum, Mittelfr , T.ii., 

 f.iii.; P. yracile, I.e., T.vii., f.l; P.enornie, I.e., T.Yii.,f.2; Turner's 

 Staw'ophanum cruciatiitu, Alg. E. Ind., T.xx., f.20-'21; and St. 

 jnisillum Turn., I.e., T.xx., f.22; and Dichotomum eleyaiis W. &, 

 G. S. West, N. Amer. Desm., PL 16, f.33, are all forms of Teir. 

 lobulahim(l!^Sig.) Hansg. So also is /". eiiorwe Ralfs, .Br. Desm., 

 T.xxxiii., f.ll, and indeed all the specimens of Tetra'edrou with 

 hyaline processes. 



Var. TKIANGULARK, n.var. (PL Ivi. , f.ll). 



Forma tetraedrica ab omui latere visa triangularis, angulis 

 bifidis in processus glabros binos productis. 



Diam. c. proc. 32; corp. 14 /x. 



In tlie figure, the fourth lobe is distorted in order to mark its 

 position plainly. The form is I'egularly tetraedricaL 



