156 Mr. J. Ralfs on the British Desniidiese. 



minute points ; end view triradiate. Euastrum, No. 13, Bailey in 



American Bacillaria, pi. 1. fig. 2 — 5. 



Boggy pools, Dolgelley and Penzance. 



Fronds rough witli minute granules^ deeply constricted in the 

 middle ; segments two or three times longer than broad, and taper- 

 ing on each side into a slender, straight and colom-less process, 

 which is terminated apparently by three minute points : Mr. Jenner, 

 however, informed me that the processes really terminate in four 

 points, although this can only be ascertained when a process is so 

 situated as to present its extremity to the observer. On the pro- 

 cesses the granules are more conspicuous and arranged in trans- 

 verse lines. The end view is triradiate, and the colouring matter 

 is confined to the centre, and forms three rays which often appear 

 bifid. 



Staurastrum gracile differs from S. tricorne in its slender pro- 

 cesses, minutely trifid at the apex. The end view somewhat re- 

 sembles that of S. paradoxum, but this species is easily distin- 

 guished by the parallel processes of its front view. 



Plate XI. fig. 3. -5*. gracile : a, front view; 6, end view ; c, empty seg- 

 ment. 



9. S. aculeatum, Mgh. Fronds spinulose ; segments in the front 

 view with a process on each side, terminated by three minute 

 spines ; end view triradiate. Mgh. I. c. p. 226. Desmidium acu- 

 leatum, Ehr. Infus. p. 142. tab. 10. fig. 12 ; Pritch. Infus. p. 184. 



/8. End view quadrangular, with four distorted rays. 



In pools and slow streams. Cross- in- Hand, Sussex, Mr. Jenner ; 

 Dolgelley. 



/3. Woking Common, Surrey, and Piltdown Common, Sussex, Mr. 

 Jenner', Penzance. 



Fronds spinulose, much constricted in the middle ; segments 

 broader than long, and having at each side a hyaline process 

 which is terminated by three minute spines and frequently dis- 

 torted. The end view is triradiate. 



The acute, conic spines, scattered over the surface, sufficiently 

 mark the present species. 



Platii; XI. fig. 4. S. aculeatum : «, front view; h, frond dividing; c, end 

 view ; d, end view of four-rayed variety ; e, empty frond. 



10. S. dilatatum, Ehr. Fronds rough ; end view with four short, 

 broad, truncate and entire rays. Ehr. Infus. p. 143. tab. 10. fig. 13 ; 

 Pritch. Infus. p. 185. figs. 100 and 101 ; Menegh. /. c. p. 227. 

 In pools amongst aquatic plants. Rusthall Common near Tun- 

 bridge Wells, and Rackham Common near Pulborough, Sussex, Mr, 

 Jenner; Dolgelley. 



Fronds very minute, rough, with minute granules, deeply con- 

 stricted in the middle, the sinuses rounded; segments trans- 



