DESMIDIUM. 245 



ing processes : in vertical view triangular or bilobed, 

 with a slight constriction beneath each angle, angles 

 rounded, slightly produced, sides straight, or slightly 

 convex. 



Zygospore unknown. 



Length 17-21 ^ ; breadth 31-35 \L ; breadth of 

 isthmus 13-5-22 pi ; breadth of apices 14-15'opi. 



IRELAND.- -Plankton of small lake between Clifden 

 and Eoundstone, Galway. 



Geogr. Distribution. Finland. Norway. Ceylon. 

 Australia. 



This plant presents a great similarity in appearance to Spondy- 

 losimn pulchrum Arch., especially the bilobed form. The short 

 connecting processes on the apices of the semicells are, however, 

 sufficient to distinguish it readily from that species. Moreover, 

 the lateral lobes of the semicells are different from those of any 

 form of Sp. pulchrum. 



It has also a considerable resemblance to Streptonema trilo- 

 batum Wallich, but differs entirely in the nature of the connections 

 between the cells, which are those of a true Desmidium. A gap 

 of some considerable size is generally evident between the apices 

 of any two contiguous cells. The filaments are usually enveloped 

 in a thick mucous sheath. 



3. Desmidium occidentale W. & G. S. West, 

 (PL CLXIV, fig. 11.) 



Desmidium occidentale West & G. S. West, Further Contrib. Plankt. Scott. 

 Lochs, 1905, p. 505, t. 6, f. 3, 4 ; Borge, Sao Paulo Alg. 1918, p. 75, t. 6, 

 f. 12. 



Cells of medium size, 1^ times broader than long, 

 slightly constricted, sinus narrow, sublinear ; semicells 

 oblong semielliptical, lateral margins gently biundulate, 

 angles rounded, apex truncate-convex, with extremely 

 short connecting processes ; cavities between the cells 

 small or wanting ; in vertical view triangular, sides 

 nearly straight or slightly convex, angles slightly pro- 

 duced and rounded. Chloroplasts axile, one in each 



