BRITISH DESMIDIEiE. 193 



to outnumber its companions. I must however observe, that specimens thus 

 obtained are more variable in their characters than such as are gathered in 

 their native abodes, and that their cells are frequently more or less distorted. 



Length of cell y^Vir ^^ ^^^ "^^^ ' breadth -gaVo • 



Tab. XXXI. fig. 15. a, h, c. different states of frond. 



5. ^. obtusus (Meyen); cells three to eight, ovate or oblong, and 

 arranged in one row, or, after division, alternately in two rows. 



Achnanthes quadralterna et octalterna, Turp. Diet, des Sc. Nat. par Lew. 

 Atl. Veg. res. f. 7, 8 (1820). 



Scenedesmus obtusus, Meyen, Nov. Act. Acad. Nat. Cur. v. 14.f. 31 (1828). 

 Meneghini, Synop. Desmid. in Linncea 1840, p. 208. Ralfs, Annals of 

 Nat. Hist. V. 15. p. 404. t. 12. f. 8 ; Trans, of Bot. Soc. of Ediiiburgh, 

 V. 2. p. 162. t. 15. Kutzmg, Phy. Germ. p. 139. Hassall, ^nY. Fresh- 

 water Alga;, p. 394. 



Scenedesmus quadraJternns, KUtz. Synop. Diatom, in Linnaa 1833, p. 608. 

 f. 94. 



Scenedesmus octoalternus, Kiitziug, I. c. p. 609. f. 95. 



Arthrodesmus acutusl, Bailey, Amer. Journ. of Science and Arts, v. 41. 

 p. 292. t. 1. f. 18 (1841). 



Common. Dolgelley and Penzance, J. R. Storrington and Beckley Fur- 

 nace near Battle, Sussex ; Reigate, Surrey ; and near Southampton, Mr.Jenner. 

 Bristol, Mr. Thwaites. Manchester, Mr. Williamson. Ambleside, Mr. Side- 

 botham. Aberdeenshire, Mr. P. Grant. 



Germany, Kiitzing. Falaise, Brebisson. Maine to Virginia, and in the 

 Mississippi River, Bailey. 



Frond minute, composed of from three to eight ovate or ovato-oblong cells 

 with rounded ends. The endochrome is very pale green. 



This species is rarely met with in a simple state, but as the cells after divi- 

 sion are still retained in connection by the mucous matrix, two rows are usually 

 present, the broader ends of one row lying between the cells of the other. 

 The hyaline matrix is frequently their only bond of union, and in this state 

 they seem to connect the Desmidieae with the Ulvacese through Merismo- 

 pedia. 



Length of cell from ^3^3^ to Y^in ^^ ^^^ ^ach. ; greatest breadth from ^oW 

 to 1 



''^ 3 6 2 3' 



Tab. XXXL fig. 16. a, b. ordinary state of frond ; c. frond just divided. 



6. S. duplex (Kiitz.) ; cells slender, fusiform, sigmoid, tapering at 

 each end into a fine point ; after division closely connected for about 

 half their length, 



Rhaphidium duplex, Kiitzing, Phycologia Germanica, p. 144 (1845). 

 Penzance, J. R. 

 Germany, Kiitzing. 



Cells linear-lanceolate ; extremities tapering to a fine point and curved in 

 opposite directions. The cells after division remain closely united ; frequently 



