14 Transactions of the Society. 



Closterium intermedium Ealfs. 

 „ juncidum Ealfs. 

 „ cornu Ehrb. 

 „ acutum Breb. 



Zygnemace^. 



Zygnema cruciatum Cleve. Fig. 27. 



This is mucb the commonest species of the order in the moun- 

 tain streams. It was rarely seen in conjugation ; and in lateral 

 conjugation not at all. Measurements showed in some instances 

 the female cells distinctly larger than the male cells ; in others 

 there was no appreciable diflference. In several instances one male 

 filament was seen in conjugation with two female filaments, never 

 the reverse. In one instance a zygosperm was seen germinating 

 while still inclosed in the parent filament ; and then, in harmony 

 with observations previously made on Spiropyra* the direction of 

 the germinating filament was at right angles to the axis of the 

 parent-cell. This was the more remarkable, as the zygosperm is 

 in this species quite spherical. 



Zynfnema Hassallii mihi (Tyndaridea anomala Hass. ; 

 Zygnema anomalum Cooke, not Ktz.). Figs. 28-30. 



Cells 52 /x in length, 28 fi in breadth ; zygosperm perfectly 

 spherical, 20 • 5 /x in diameter, olive-green to emerald-green. This 

 species is common in roadside runnels, and presents several dis- 

 tinctive characters from others of the genus. In the non-con- 

 jugating and most frequent condition (fig. 28), the cells are almost 

 entirely filled up by a dark-green endochrome ; it is only when 

 about to conjugate (fig. 29) that it becomes difierentiated into two 

 stars ; and then not so distinctly as in Z. cruciatum. The mucous 

 sheath by which the filaments are invested is distinctly visible at 

 all stages. Conjugation seems to take place only when the fila- 

 ments are nearly dried up, and has apparently only been observed 

 in this country by Hassall, Ealfs, and Jenner. I can entirely 

 confirm the statement of these observers that the zygosperms are 

 formed in one of the conjugating filaments (fig. 30) ; Kiitzing's 

 species, in which they are formed m a canal between the filaments, 

 must, therefore, be a different one. I think, however, Hassall is 

 in error in figuring the zygosperms as formed indifferently in either 

 filament ; this is quite contrary to numerous observations of my 

 own. 



Spirogyra porticalis Vauch. 

 „ longata Vauch. 

 tenuissima Hass. 



* Journ. Linn. Soc. (Bot.) xx. (1884) p. 430. 



