HYALOTHECA. 239 



gatse. It is also more frequently found in plankton than in 

 collections from bogs. Its chloroplasts are rather unusual for 

 the genus Hyalotheca, although chloroplasts of this type occur, 

 amongst other Desmidiacese, in the genus Mesotcenium. 



In addition to zygospores, the formation of aplanospores has 

 been observed in this species. The filaments partially dissociate 

 into individual cells during their formation. The cell-contents 

 round themselves off, and finally acquire a thick cell-wall, which 

 is yellowish and distinctly punctate when mature. The aplano- 

 spores are elliptical with acutely-rounded poles. Thus they are 

 very different in appearance from the zygospores. 



5. Hyalotheca undulata Xordst. 

 (PL CLXII, figs. 6-9.) 



Hyalotheca undulnta Xordst. in Wittr. & Xordst. Als. exsic. 1879, no. 248, 

 and in fasc. 21, 1889, p. 33 ; Wolle. Desm. U. S. 1884, p. 23, t. 53, f. 8 ; 

 De Toni, Syll. Alg. 1889, p. 788 ; West, Freshw. Alg. X. Wales, 1890, 

 p. 7 (sep.); Alg. \V. Ireland, 1892, p. 117; Roy & Biss. Scott. Desm. 

 1893, p. 9, t. 1, f. 1 ; West & G. S. West, Some N. Amer. Desm. 1896, 

 p. 232 ; Freshw. Chloroph. Koh Chang, 1901, p. 96 ; Alg. Ceylon, 1902, 

 p. 195, t. 22, f. 27 ; Alg. Burma, 1907, p. 226. 



H. undulata var. producta Turner, Freshw. Alg. E. India, 1893, p. 152, t. 18, 

 f. 15. 



Cells very small, li-2 times longer than broad, lateral 

 margins with a broad shallow median indentation, so 

 that they are biimdulate ; semicells globose-obovate, 

 with truncate apices ; diameter of isthmus and apex 

 of semicells about equal ; cells in end view circular ; 

 chloroplasts axile, one in each semicell, each with a 

 central pyrenoid and about 4 radiating ridges. The 

 filaments may or may not be enclosed in a gelatinous 

 sheath. 



Zygospore unknown. 



Length 10 -17 '5 pi ; breadth 6-9 ^ ; diam. isthmus = 

 diam. apices = 4'6-7'5 \L. 



WALES. Capel Curig, Carnarvonshire ! In the plank- 

 ton ! 



SCOTLAND.- -Birsemore Loch, Aberdeen (Roy & Biss.). 



IRELAND.- -Lough Anna, Donegal ! Roundstone, Bally- 

 nahinch. and in the plankton, Gal way ! Upper Lake of 

 Killarney and Lough Guitane, Kerry ! Adrigole, Cork ! 



