BRITISH DESMIDIE/E. 179 



1. S. condensata (Breb.) ; endochrome a single, broad, closely spiral 

 band. 



Spirotcenia condensata, Brebisson, in lit. cum icone (1846). 



Common. Dolgelley and Penzance, J. R. Henfield, Sussex, and bogs at 

 Fisher's Castle, Tunbridge Wells, Mr. Jenner. Ayrshire, Rev. D. Lands- 

 borough. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. 

 Sidehotham. Near Bristol, Mr. Thivaites. 



Falaise, Brebisson. 



Frond bright yellow-green, cylindrical with rounded ends, or fusiform, five 

 to ten times longer than broad, enclosed in an evident mucous covering. The 

 endochrome consists of a single broad spiral band. The revolutions are close, 

 and from seven to twelve in number. 



This is a beautiful plant ; and in a recent state the spiral arrangement of the 

 endochrome is very conspicuous, but it collapses shortly after being gathered. 



Length of frond ^-i-g- of an inch ; breadth yoT»- 



Tab. XXXIV. fig. 1. a, b. mature frond ; c. fronds after division. 



2. S. obscura ; endochrome at first in several slender spiral 



threads, afterwards uniform. 



Dolgelley and Penzance, J. R. Bogs at Fisher's Castle, Tunbridge Wells, 

 Mr. Jenner. 



Frond dark green, cylindrical or fusiform, extremities attenuated, five to 

 eight times longer than broad. When young the endochrome is distinctly 

 spiral, and the frond resembles a joint of a many-spired species of Zygnema. 

 The threads or fillets are several in number, slender, and each of them makes 

 but one or two revolutions in the length of the frond. Generally however the 

 endochrome forms a uniform dark green mass without any appearance of 

 spires. In this state, a small hyaline space left at each extremity will fre- 

 quently be found to contain a small granule. 



I long regarded this species as probably a variety of Spirotcenia condensata, 

 nor was it until I met vdth a yomig specimen that I was fully satisfied of its 

 distinctness. Even specimens which do not exhibit the spires may be recog- 

 nized by the darker colour of their endochrome and more tapering extremities. 



Length of frond from -^^ to -^ of an inch ; greatest breadth from y oVo 



to 



9oT* 



Tab. XXXIV. fig. 2. a, b, c. single fronds ; d, e. fronds after division. 



*** Cells fasciculated. 

 18. ANKISTRODESMUS, Corda. 

 Cells elongated, attenuated, entire, aggregated in faggot-like bundles. 

 The cells are fusiform or crescent-shaped, have no constriction at 



