156 Mr. J. Ralfs on the British Desniidicre. 



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



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



Boggy pools, Dolgelley and Penzance. 



Fronds rough with, 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. Jenuei', 

 howe^■er, 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 \\e\y is triradiate, and the colom-ing 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 \dew somewhat re- 

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

 guished by the parallel processes of its front ^dew. 



Plate XI. fig. 3. S. gracile : a, front view ; b, end view ; c, empty seg- 

 ment. 



9. S. acideatum, Mgh. Fronds spiuulose ; segments in the front 

 ^■iew 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. 



/3. End view quadrangular, with four distorted rays. 



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

 Dolgelley. 



ft. 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 

 Mhich is terminated by three minute spines and frequently dis- 

 torted. The end ^-iew is tiiradiate. 



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

 mark the present species. 



Plate XI. fig. 4. S. acideatum : a, front view; b, frond dividing; r, 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 ravs. Ehr. Infus. p. 143. tab. 10. fig. 13 ; 

 Pritch. Infus. p. 185. figs. I'OO and 101 ; Menegh. I. 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 gi-anules, deeply con- 

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



