156 BRITISH DESMIDIE^. 



dulations, which are more numerous and equal, depend on the presence of 

 whorls of small tubercles. In D. coronatum, Brel)., the apex behig encircled 

 by a series of small tubercles, the end view is crenate. 



Length of frond -g\ of an inch ; breadth -^ ; breadth at hiflation -^ ; 

 breadth at end ■^^. 



Tab, XXVI. fig. 1. a. frond with endochrome ; b, empty frond. 



2. D. truncatum (Breb.) ; frond stout ; segments three or four times 

 longer than broad, with a single inflation at the base, tapei'ing to the 

 truncate entire ends ; suture projecting on each side. 



Closterium truncatum, Breb. Meneghini, Synop. Desmid. in Linncea 1840, 



p. 235. 

 Docidium truncatum, Brebisson, in lit. cum icone (1846). 



Carnarvon and Penzance, /. R. Hastings, Sussex, and Brookland near 

 Reigate, Surrey, Mr. Jenner. 



Falaise, Brebisson. Germany, Kiitzing. 



Frond cylindrical, stout, distinctly constricted at the middle, the suture 

 forming a thickened rim, which pi'ojects on each side like a small point. Seg- 

 ments three or four times longer than broad, slightly inflated at the base and 

 tapering towards the end, which is truncate and entire. 



Docidium truncatum seems to me to approach closely to D. nodulosum, 

 with which it agrees in size. Its distinctive marks are the more attenuated 

 extremities and the solitary inflation at the base of each segment, so that its 

 margins are not undulated. Mr. Jenner considers them as undoubtedly distinct, 

 but to which dried specimens belong I am occasionally unable to decide ; for 

 in drying, fronds of D. nodulosum frequently become attenuated at the ends, 

 and sometimes only the basal inflation can be seen. Its larger size, short- 

 ness of the segments in comparison with their breadth, and the distinct projec- 

 tion of the junction-rim on each side, sufficiently distinguish D. truncatum 

 from D. Ehrenbergii. 



Length of frond from -^ to -jL. of an inch ; greatest breadth from -^^ to 

 ■^^ ; breadth at constriction -g-iy ; breadth at end from yjVs ^o q^to • 



Tab. XXVI. fig. 2. a. frond with endochrome ; b. empty frond. 



3. D. clavatum (Kiitz.) ; segments many times longer than broad, 

 with a single inflation at the base ; end clavate, but truncate at the 

 apex. 



Closterium truncatum, Kutzing, Phy. Germ. p. 133 (1845), nee Breb. 

 Docidium clavatum, Kiitzing, in lit. cum icone (1840). Brebisson, in lit. cum 

 icone et spccimine. 



Midhurst, Sussex, Mr. Jenner. 



Germany, Kiitzing. Falaise, Brebisson. 



Frond longer than those of the first two species, but more slender, constricted 

 at the middle ; the suture strongly marked, but not projecting at the margin. 



