238 BRITISH DESMIDIACE^E. 



4. Hyalotheca neglecta Kacib. 

 (PL CLXII, figs. 11-15; PL CLXIII, figs. 1-4.) 



Hyalotheca neglecta Racib. Desm. Tapakoomas, 1895, p. 30, t. 2, f. 2, 3 ; 

 'West & G. S. West, Alg. S. England, 1897, p. 497 ; Obs. Conj. 1898, 

 pp. 52, 54, t. 4, f. 22-33; Desm. U. S. 1898, p. 321 ; G. S. West, Brit. 

 Freshw. Alg. 1904, p. 176, f. 68, E-H ; West & G. S. West, Further 

 Contrib. Plankton Scott. Lochs, 1905, t. 5, no. 6, f. 1. 



Cells of medium size, 2-13 times longer than broad, 

 subcylindrical, with, an almost imperceptible median 

 constriction, and a slight inflation on either side of it ; 

 apices broad and truncate ; cells in vertical view 

 circular, cells closely united to form short filaments, 

 often enclosed in a broad gelatinous sheath. Cell-wall 

 minutely punctulate, punctse arranged in transverse rows. 

 Chloroplasts axile, one in each semicell, typically with 

 a single central pyrenoid in each, and plate-like, so that 

 when viewed from the edge it seems very narrow, just 

 as in Mougiotia. 



Zygospores formed after the filaments have dis- 

 sociated into individual cells, rounded, walls smooth, 

 but sometimes with two rounded mamillse at opposite 

 poles. 



Length 28-42 [JL ; breadth 11 '5-14^ ; diam. zygosp. 

 23-28 (JL. 



ENGLAND.- -Plankton of Easedale Tarn, Westmore- 

 land ! Thursley Common, Surrey ! New Forest, Hants 

 (with zygospores) ! 



WALES. Capel Curig, Carnarvonshire ! In the plank- 

 ton ! 



SCOTLAND.- -Ehiconich, and in the plankton of Lochs 

 Shin and Ruar, Sutherland ! Loch Shiel, Inverness ! 

 Plankton of Lochs Fadaghoda, an Sgath and Stranabhat, 

 Lewis, Lochs Diracleet and Laxadale, Harris, and Loch 

 nan Eun, N. Uist, Outer Hebrides ! 



IRELAND.- -Plankton of Gal way ! 



Geogr. Distribution. Norway. Ceylon. United States. 

 Guiana. 



This is one of the rarest of Desmids, and might easily be over- 

 looked owing to its great similarity to other filamentous Conju- 



