532 PLANKTON OF THE SYDNEY WATER-SUPPLY, 



interdum spinis singulis, interdum verrucis simplicibus aut bifidis 

 utrinque instructse; centre serie granulorum 6 concentrice dis- 

 posita ornatse. 



Long. c. proc. 27, s. proc. 15; lat. c. proc. 50 isth. 6 /x. 



St. orbiculare var. MUTicuM(Ralfs) mihi. 



Forma mixta : - type + var. vmvticum,. 

 Long. 38; lat. 32; isth. 14 /x. 



*S'^. muticum is only a growth-form of St. orbiculare; mixed 

 forms are quite common. 



Var. protractum, n.var. (PI. liv., f.25). 



Semicellulse semi-ellipticae, subtriangulares, interdum adpressae; 

 basi planse; angulis lateralibus late-rotundatis; lateribus leniter 

 arcuatis; apicibus levissime acuminatis. 



Long. 43-48; lat. 47 [x. 



This form was first found at Collectof. In the plankton, it 

 was noted as a mixed form with the type, both, however, with 

 incipient processes. Cf. Ralfs, Br. Desm., T.xxi., f.5h; and Roy 

 & Bisset, Jap. Desm., f.l4, of which it is a forma major. 



Var. PLANKTONicuM, n.var. (PI. liv., f.27). 



Forma minuta sinu aperto valde constricta; semicellulse semi- 

 ellipticse, angulis inferioribus paullulo quadratis; lateribus e basi 

 plus minus rectis; apicibus leniter arcuatis. A vertice triangu- 

 lares; lateribus valde retusis; angulis paullo quadratis, lateribus 

 parallelis, apicibus subtruncatis rotundatis. 



Long. 20; lat. 15; isth. 7 /x. Common. 



Cf. Schmidle, Schwarz. u. Oberrh., Fig. iv., 1. 



MYXOPHYCE^. 



Genus SCYTONEMA Ag. 



ScvT. MiRABiLE(Dillw.) Bomet, Bull. Soc. P>ot. Fr. xxxvi., 1889. 



Lat. fil. 18-20; lat. trich. 6-8; heterocyst. long. 14-16, lat. 10-12; 

 cell. veg. alt. 4-12 /x. 



8yn., Scytonema Jiguratum Ag. (PI. Ivi., f.l3a,6,c). 



