92 BRITISH DESMIDIACE.E. 



stricted, sinus very widely open, semicells subspherical ; 

 lateral margins produced into long, straight, and smooth 

 processes, which diverge from those of the other semicell ; 

 apex of processes usually forked into two obtuse teeth, 

 but sometimes entire and obtuse. Vertical view 4-5- 

 radiate, processes as long as the ' body : ' of the semicell ; 

 cell-wall smooth ; processes of one semicell alternating 

 with those of the other. Chloroplast axile with a large 

 central pyrenoid. 



Zygospore unknown. 



Length, without processes, 31-37 \L ; with processes, 

 40-44 [ji ; breadth, without processes, about 20-22 y. ; 

 with processes, 53-61 pt ; breadth of isthmus 15-1 5 '5 u. 



SCOTLAND.- -Plankton of Loch Fadaghoda, Lewis, 

 Outer Hebrides ! 



St. subnudibmchiatum is very similar to St. brachiatum Rails 

 in the nature of its processes, but it differs widely from that 

 species in the form of its semicells, and its slight constriction. 

 The processes are variable in character, even in the same speci- 

 men. They are usually bifurcate at the extremity, each lobe 

 being rounded, but sometimes they are obtuse and entire. 



It also has some superficial resemblances to St. Clevei (Wittr.) 

 Boy & Biss., from which it is readily distinguished by its broader 

 isthmus, by the rounded apical teeth of the processes, and by 

 the fact that the latter lie all in the same plane. 



110. Staurastrum laeve Ralfs. 

 (PL CXLI, figs. 1-3.) 



tit.lceve Ralfs, Brit. Desm. 1848, p. 131, t. 23, f. 10 ; Arch, in Pritch. Infus. 

 1861, p. 743 ; Rabenh. Krypt. Flor. Sachs. 1863, p. 193 ; Flor. Europ. 

 Alg. 1868, p. 206 ; Wittr. Gotl. Ol. sotv. Alg. 1872, p. 54 ; Kirchn. Alg. 

 Schles. 1878, p. 167 ; Cooke, Brit, Desm. 1887, p. 180, t. 63, f. 2 ; Hansg. 

 Prodr. Algenfl. Bohm. 1888, p. 212 ; De Toni, Syll. Alg. 1889, p. 1227 ; 

 Roy & Biss. Scott. Desm. 1893, p. 22 ; West & G. S. West, Alg. S. England, 

 1897, p. 494 ; Comere, Desm. de France, 1901, p. 152, t. 11, f. 14 ; West 

 & G. S. West, Alga-fl. Yorks. 1902, p. 104 ; Gutw. Alg. Ins. Java, 1902, 

 p. 606. 



Cells very small, about 1| times longer than broad, 

 not including the processes, deeply constricted, sinus 



