BY G. I. PLAYFAIR. 517 



Var. TETRAPEDiA(Kirchn.) mihi. (PI. Ivi., f.3). 



Syn., Staurogenia tetrapedut Kirchn. ; Tetrapedia emar- 

 ginata Schrod. ; he m m e rmannia einarginata Chod. ; Cruci- 

 geuia ietnipedia W. & G. S. West. 



Long. 8, lat.8 /x. 



Var. QUADKATUM, n.var. (PI. Ivi., f.3a). 



Cellula unica, quadrata ; angulis rotuudatis ; lateiibus 

 emarginatis ; endochroma in partes triangulares 4, cruce liya- 

 lina plus minus divisa. 



Diam. 8 /a. 



The cell itself does not divide in this form and the next. 

 The chloroplast gradually separates from the centre outwards 

 into four triangular lozenges. In PI. Ivi., f.3a, this separa- 

 tion is not yet quite complete, a little band still remaining at 

 each corner; no septa are formed. Var. tetra'pedia (PI. Ivi., 

 f.3) is the outgrowth of this form. 



Var. UNiCELLULARE, n.var. (PL Ivi., f.4). 



Cellula unica, circularis, disciformis, in centro foramine 

 instructa. Endochroma homogenea in partes 4 cru^e hyalina 

 plus minus divisa. A latere deplanata elliptica, in medio con- 

 stricta. Diam. 6 p.. 



The four preceding forms were obtained in considerable 

 numbers by filtering a few gallons of water from the pond at 

 Pott's Hill. They show the development of a four-celled 

 Pedi. tetras out of the resting cell resulting from a zoospore. 

 Crucigenia cannot stand as a genus, the species composing it 

 being all infantile growth-forms of Pedinstrum. 



Var. TRiANGULARE(Chod.) mihi, forma. (PI. Ivi., f.5). 



Long. 8, lat. 7 ji. 



Syn., Staurogenia triangxdaris Chodat. In this form, the 

 central foramen has early swelled into an oblong lacuna causing 

 the component cells to assume a somewhat different shape. There 

 is a form of Pedi. tetras also corresponding to this crucigenia-siaige, 

 the 4-celled ccenobium being rhombic instead of square. 



