12 Transactions of the Society. 



but in places the pseudo-cells were arranged in two rows, and they 

 were then smaller and nearly spherical. In the main filament there 

 were mostly two rows of nearly spherical, interspersed with a few 

 larger elliptical, pseudo-cells in a single row. The largest of these 

 pseudo-cells were about 32*5 yu, by 20 yu,. The contents of the pseudo- 

 cells were brown in the main filament, more often a light green in the 

 branches ; the entire filament externally to the pseudo-cells being also 

 filled with a hght brown endochrome. 



Following Eabenhorst, Dr. Cooke regards Stigonema as a genus of 

 hchens. Whether this view is correct or not I express no opinion; 

 but the organism here figured, which agrees with the general description 

 of the genus, unquestionably carries on an independent existence, like 

 any other fresh-water alga or protophyte. As Cooke's figure appears to 

 be taken from a dried specimen only, I have presented, by way of com- 

 parison, one from the living plant. 



NOSTOOACE^. 



*Anabaena flos-aquae Ktz. Frequent. 

 Cylindrospermum macrospermum Ktz. 



Nostoc hyalinum Benn. (Journ. li. Micr. Soc, 1886, p. 4, t. i. 

 f. 2, 3). 



This pretty Nostoc, obtained last year in the Lake District, was again 

 observed, but only once, in a bog pool at St. Denis. I am unable to 

 accept Dr. Cooke's suggestion that it is identical with N. minutissimum 

 Ktz., the mature " frond " differing from that species in size, in the 

 degree of complexity of the trichome, and in other points. 



ALa^. 



Pediastee.s;. 



Pediastrum Boryanum Turp. 

 „ Ehrenbergii Br. 



* „ rotula Br. 



* Pediastrum (Anomopedium) integrum Nag. Figs. 11-13. 



This interesting Pediastrum represents a section of the genus not 

 hitherto detected in Britain, distinguished by the peripheral cells being 

 neither lobed nor incised. The coenobium consists of 8-16-32 cells, 

 and is nearly round or irregularly oval, when mature about 125 //, long 

 by 100 /Lt broad, compact, without any intercellular lacunae. The cells 

 are very regular and thick-walled, about 25 yu, in diameter, the central 

 ones symmetrically hexagonal, the peripheral cells alternately obscurely 

 hexagonal and obscurely pentagonal, with rounded outer margin, not 

 differing in their endochrome from the central cells. In an early stage, 

 ■when the ca3nobium consists of eight cells, each peripheral cell has a 

 single central short obtuse hyaline process ; at later stages each peripheral 

 cell has usually two such processes at the obscure angles, one pointing 

 upwards, the other downwards ; but one or both may be entirely wanting. 

 On losing their hyaline processes the peripheral cells exhibit a tendency 



I 



