Mr. J. Ralfs on the British Desmidiese. 403 



species, from which it only differs in the absence of bristles on 

 the outer cells. 



Plate XII. fig. 4. Scenedesmus quadrkaudatus : b, variety /3; c, variety 

 y. ecornis. 



2. S. dimorphus, Ktz. Cells acute, four to eight, placed evenly in a 

 single row ; the inner cells fusiform, the outer externally lunate. 

 Ktz. I. c. p. 608 ; Menegh. /. c. p. 208. Arthrodesmus pectinatus, 

 Ehr. Infus. p. 150. tab. 10. fig. 17. Achnanthes dimo7pha, Turp. 

 (1820). 



Dolgelley, J. R.; near Bristol, Mr. Thwaites. 



Fronds very minute, consisting of four to eight cells placed 

 evenly side by side in a single row ; the inner cells straight, fu- 

 siform, attenuated and acute at each end, the outer ones externally 

 lunate. 



The endochrome is pale bluish green. 



Plate XII. fig. 5. Scenedesmus dimorphus, 



3. S. acutus, Meyen. *' Cells two to six, fusiform, acute at both 

 ends, unequally ventricose, arranged in a double, irregularly alter- 

 nating series." Menegh. /. c.p. 207 ; Kutz. /. c. p. 609. fig. 9Q. 

 Arthrodesmus acutus, Ehr. Infus. p. 150. tab. 10. fig. 19. c, d, 



I notice this species because the Rev. M. J. Berkeley has ga- 

 thered it near King^s Cliffe, and I have occasionally met with 

 specimens at Dolgelley which agree with Ehrenberg's figures, but 

 as I omitted to draw up a description at the time, I have bor- 

 rowed the specific character from Meneghini. 



The cells are fusiform, somewhat ventricose in the middle and 

 acute at the ends; they project more or less alternately on each 

 margin, and thus form two irregular series. When there is but 

 little irregularity and the cells are nearly in a single series, this 

 species has some resemblance to S. dimorphus, but in the latter 

 the cells are not ventricose in the middle and are arranged quite 

 evenly side by side. 



Plate XII. fig. 6. Scenedesmus acutus. 



4. S. triseriatus, Mgh. Cells elliptico-fusiform, eight arranged in 

 two oblique series, in each of which the cells are in close apposition; 

 but the outermost one, which is lunate, is not in contact with any 

 cell of the other series. Menegh. /. c. p. 208. Arthrodesmus 

 acutus, Ehr. Infus. tab. 10. fig. 19. a, b, e (according to Mene- 

 ghini) . 



King's Cliflfe, Rev, M. J. Berkeley; in a cave near Bristol, Mr. 

 Thwaites. 



In the perfect frond the cells are eight in number, arranged 

 obliquely in two distinct series. Each scries has three cells which 

 are fusiform, equal, somewhat ventricose in the middle, acute at 



