200 BRITISH DKSMIDIACE.E. 



2. Cosmocladium perissum Eoy and Biss. 

 (PL CLVIII, figs. 4-7.) 



Cosmocladium perissum Roy & Biss. Scott. Desm. 1893, p. 62, t. 2, f. 14; 

 G. S. West, Brit. Freshw. Alg. 1904, p. 173, f. 66 C. 



Cells minute, flattened, nearly as broad as long, con- 

 striction fairly deep and somewhat obtuse, opening 

 widely ; apex slightly concave, sides broadly rounded ; 

 cell-wall very pellucid and sometimes brownish in 

 colour ; end view elliptical ; cells forming free colonies. 



Zygospore large in proportion to the size of the cells, 

 extremely irregular in shape, with several irregular and 

 blunt spiny protuberances, reddish brown in colour. 



Length 12-1 3 pi; breadth 10-12^; thickness 6 pt ; 

 diam. zygospore 15-20 pi (-27 j* ; West). 



SCOTLAND. Aboyne, Aberdeen ; Cammie in Strachan, 

 Kincardine (Roy & Biss.). Clova Mts., Forfar ! 



This species never forms very large colonies, and more than 

 4 cells are scarcely ever found together. The cells occur in a 

 simple row, loosely joined by very delicate gelatinous threads. 

 The semicells have only two jelly-secreting pores each, one on 

 either side of the isthmus, whereas both Cosmocladium constrictum 

 and C. Saxonicum have quite a well-developed series of pores. 

 This very slight development of secreting pores is responsible 

 for the extreme delicacy of the connecting strands, and the small 

 size of the colonies in C. perissum as compared with the two above- 

 mentioned species. 



3. Cosmocladium pulchellum Breb. 

 (PL CLVIII, figs. 11, 12.) 



Cosmocladium pulchellum Breb. Liste Desm. 1856, p. 133, t. 1, f. 20; De 

 Bary, Conj. 1858, p. 77; Ueber Cosmocladium, 1865. p. 329; Rabenh. 

 Flor. Europ. Alg. 1868, p. 54 ; Kirchn. Alg. Sehles. 1878, p. 10f> ; De 

 Toni, Syll. Alg. 1889, p. 804; Roy & Biss. Scott. Desm. 1893, p. 62; 

 Comere, Desm. de France, 1901. p. 180, t, 15, f. 15; G. S. West, Brit. 

 Freshw. Alg. 1904, p. 173, f. 66 B. 



Cells small, somewhat longer than broad, deeply 

 constricted, sinus narrow but opening more widely; 

 semicells elliptical or subreniform; vertical view ellip- 



