30 BRITISH DESMIDIACE^. 



This genus, although widely distributor! throughout the 

 British Islands, is not really common, nor is it partial to any 

 particular kind of district. The filaments, which are some- 

 times of great length, are exceedingly fragile, and a slight 

 disturbance of the water is usually sufficient to cause them to 

 break up into their individual cells, each of which then lives a 

 free and independent existence. There are usually two chloro- 

 plasts in each cell, the small space between them in the centre 

 of the cell being occupied by a certain amount of colourless 

 protoplasm containing the nucleus. When only one chloro- 

 plast is present the nucleus is situated in the median portion 

 of the cell in a lateral position. A terminal vacuole containing 

 a group of minute moving granules is sometimes present a~t 

 each end of the cell ; this is best observed in G. Kinakuni. 



1. Gonatozygon monotsenium De Bary. 

 (PL I, figs.1-7 ; PI. V, fig. 5.) 



Docidium? asperum Ealfs, Brit. Desm. 1848, p. 158, t. xxi, f. 6 a, b. 



Gonatozygon monotsenium De Bary, in Eabenh. Alg. 1856, no. 539. 



G. Ralfsii De Bary, Conj. 1858, p. 76, t. iv, f. 23-25; Archer, in Pritch. 

 Infus. 1861, p. 721, t. iii, f. 1-2 ; Eabenh. Flor. Eiu-op. Alg. 1868, III, 

 p. 107; Cooke, Brit. Desm. 1886, p. 2, t. i, f. 1 ; Eoy A Biss. Scott. 

 Desm. 1894, p. 250 ; West and G. S. West, Alga-fl. Yor'ks. 1901, p. 39. 



Leptocystinema asperum Archer, Suppl. Cat. Desmicl. 1858, v, p. 251, t. xxi, 



I. 5. 



Gonatozyrion asperum Eabenh. Krypt. Fl. Sachs. 1863, p. 181 ; Wolle 

 Desm. U.S. 1884, p. 22, t. i, f. 1. 



Cells 10-25 times longer than their diameter, cylin- 

 drical, apices slightly dilated ; cell-wall minutely and 

 densely granulate ; grannies variable, sometimes veiy 

 indistinct, sometimes strong and sharp, even papilli- 

 forra. Pyrenoids about six to nine in eacb chloroplast. 



Zygospore globose and smooth. 



Length 82-284 /t ; breadth 7-5-11-5,1 ; breadth of 

 apices 8'6-12-5^; diam. zygospore 25-28 /u. 



ENGLAND. Cumberland! Westmoreland! (Bissett). 

 W., N., and E. Yorks ! Zygospores from Cnllingworth 

 and Cantley Spont. Cheshire (Roy). Leicester (Roy). 

 Cambridge! Surrey! Hants! (Roy). Devon! Corn- 

 wall! (Marquand). 



WALES. Capel Curig ! (GooJce and Wilh), Llyn 

 Ogwen and Llyn Padarn, Carnarvonshire ! 



