Mr. J. Haifa on the British Dcsiuidicju. 403 



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

 the outer cells. 



Plate XII. lig. 4. Scencdesmus quadricaudatus : 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. /. c. p. 60S ; Mcncgh. I. c. p. 208. Arthrodesmus pectinatus, 

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

 (1820). 



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



Fronds very minute, consisting of four to eight cells ])laced 

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

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

 lunate. 



The endochrome is pale bluish gi'cen. 



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, irregidarly alter- 

 nating series." Menegh. /. c. p. 207 ; Kutz. /. c. p. 609. fig. 1)6. 

 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 Mencghini. 



The cells arc 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. A^Tien 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. 5. triseriatus, Mgh. Cells elliptico-fusiform, eight arranged in 

 two obhque series, in each of which the cells are in close ap])osition ; 

 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 Cliffe, Rev. M. J. Berkeley, in a cave near Bristol, Mir. 

 Thwaites. 



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

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

 are fusilbrm, equal, somewhat veutricose in the middle, acute at 



