150 BRITISH DESMIDIE^. 



are very minute, and resemble puncta ; hence the margin of the frond is entire. 

 The puncta or granules are arranged in longitudinal lines, hut those in the 

 same line are so close together that they are nearly, if not quite, confluent ; in 

 fact, unless a very high power of the microscope be used, the frond appears 

 simply striate. Besides the central suture, several other transverse lines di^^lde 

 the empty frond into compartments. This fonn agrees best withEhrenberg's 

 figure of Closterium margaritaceum, but it is not denticulate at the margin. 



Sporangia of y. have been gathered by myself near Dolgelley, and those of 

 (j. by Mr. Thw^aites near Bristol. Both are orbicular, and situate betvpeen 

 the deciduous fronds. 



Length of frond in a. yig- of an inch ; breadth -g^ ; breadth at constric- 

 tion YXsZ ; length of frond in y. yi-g ; breadth yiVs '■> diameter of sporan- 

 gium ^. 



Tab. XXV. fig. 1. a. frond of a. with endochrome ; b, c. empty fronds; 

 d. empty frond of y. as seen under a low power ; e,/. fronds with endochrome ; 

 ff, h. sporangia. 



Tab. XXXIII. fig. 3. sporangium of /S. 



2. P. Cylindrus (Ehr.) ; frond cylindrical with rotundato-truncate 

 ends, rough with scattered pearly granules. 



Closterium 1 Cylindrus, Ehrenberg, In/us. p. 95. t. 6. f. 6 (1838). Meneghini, 



Si/nop. Desmid. p. 236. Kiitzing, Phy. Germ. p. 132. 

 Penium Cylindrus, Bre'bisson, in lit. (1846). 



Dolgelley, J. R. Ambleside, Mr. Sidehotham. Henfield ; Ashdown 

 Forest, and Piltdovvai Common near Uckfield, Sussex, Mr. Jenner. 



Berlin, Ehrenberg. Falaise, Brebisson. 



Frond very minute, smaller than that of Penium margaritaceum, two or 

 three times longer than broad, cylindrical with truncate ends, and rough with 

 minute scattered granules or apiculi. As the covering is usually of a deep 

 rusty red, it obscures the view of the endochrome. I have not observed any 

 terminal globules. 



Penium Cylindrus resembles P. margaritaceum in form, but is much smaller, 

 and its pearly granules are scattered and not arranged in lines. The red co- 

 lour of the empty frond is darker than that of any other plant in the family. 



I have little hesitation in referring the British specimens to Ehrenberg's 

 Closterium Cylindrus, although in their scattered granules they diifer from his 

 and Meneghini' s descriptions. 



Length of frond -~-^ of an inch ; breadth yyVo • 



Tab. XXV. fig. 2. a. frond with endochrome ; b. dividing frond ; e. empty 

 frond. 



** Frond smooth, colourless. 

 f Sporangium situated between the deciduous cells. 



3. P. Digitus (Ehr.); frond smooth, elliptic-oblong M'ith rounded 

 ends ; fillets obscure, undulated, interrupted only by a transverse 

 band at the suture. 



