BRITISH DESMIDIEiE. 191 



2. S. dimorphus (Turp.) ; cells acute, four to eight, placed evenly in a 

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



Achnanthes dimorpha, Turp. Diet, des Sc. Nat. par Leer. Atl. Veg. ves. f. / 

 (1820). 



Scenedesmus pectinatiis, Meyen, Nov. Act. Acad. Nat. Cur. \. 14. p. 2. f. 34, 

 35 (1828). ILnizm^,' Sijnop. Diatom, p. 608; Phij. Germ. p. 140. 

 Brebisson in lit. 



Scenedesmus dimorjikus, Kiitzing, Synop. Diatom, in Linncea 1833, p. 608. 

 IMeiieghini, Synop. Desmid. in Linncea 1840, p. 208. Ralfs, Anttals of 

 Nat. Hist. V, 15. p. 403. t. 12. f. 5 ; Trans, of Bot. Soc. of Edinburgh, 

 Y. 2. p. 160. t. 15. Hassall, Brit. Freshwater Algce, p. 393. 



Arthrodesmus pectinatus, Ehr. Infus. p. 151. t. 10. f. 17 (1838). 



Dolgelley and Penzance, /. R. Bristol, Mr. Thwaites. Manchester, Mr. 

 Sidebotham and Mr. Williamson. Aberdeen, Mr. P. Grant. Weston Bogs 

 near Southampton, Mr. Jenner. 



Germany, Kiitzing, Ehrenberg, Corda, &c. Falaise, Brebisson. 



Frond very minute, consisting of four to eight cells placed evenly side by 

 side in a single row ; the inner cells straight, fusiform, attenuated, and acute 

 at each end ; the outer ones externally lunate. The endochrome is pale bluish- 

 green. 



Length of cell from yoVo ^*^ ^h^ °^ ^^^ ^''^'^^^ '■> breadth -g-iVo • 

 Tab. XXXI. fig. 13. a. frond with endochrome ; b. empty frond. 



3. S. acutus (Meyen) ; cells two to eight, fusiform, acuminate, arranged 

 in a single, irregularly alternating series. 



Scenedesmus acutus, Meyen, Nov. Act. Acad. Nat. Cur. v. 14. t. 43. f. 32 

 (1828). Kiitzing, 'Synop. Diatom, in Linncea 1833, p. 609. f. 96; 

 Phycologia Germanica, p. 139. ^leneghini, Synop. Desmid. in Linncea 

 1840, p. 207. Ralfs, Annals of Nat. Hist. v. 15. p. 403. t. 12. f. 6 ; 

 Trans, of Bot. Soc. of Edinburgh, v. 2. p. 160. t. 15. Hassall, Brit. 

 Freshwater Algce, p. 393, 



Scenedesmus fusiformis, Meueghini, Consp. Alg.Eugan. p. 18 (1837) ; Synop. 

 Desmid. in Linncea 1840, p. 208. 



Arthrodesmus acutus, Ehrenberg, Infusor. p. 150. t. 10. f. 19 (1838). 



King's CliflPe, Northamptonshire, Rev. M. J. Berkeley. Bristol, Mr. 

 Thwaites. Dolgelley, J. R. Weston Bogs near Southampton, Mr. Jenner. 



Germany, Ehrenberg, Kiitzing. Falaise, Brebisson. 



Cells fusiform, acute at each end, frequently more or less ventricose ; after 

 division forming a single series, but projecting alternately more or less on each 

 margin. The two outer cells are frequently crescent-shaped. 



When the cells are nearly uniform tliis species has some resemblance to 

 Scenedesmus dimorphus ; but in the latter the cells are more slender, never 

 ventricose, and are arranged quite evenly side by side. It is more difficult to 

 distinguish S. acutus from S. obliquus, and I am far from certain that Ehren- 

 berg erred in uniting them. The principal distinction is that in S. acutus 



