190 niirTTSH DESMIDTAOE^E. 



Cells with shorter apical processes than in the 

 typical form, tlie body of the cell being- gradually 

 attenuated to the apices; striffi often scarcely dis- 

 cernible. 



Length 1 88-3 65 ^ ; breadth 18-27 p- ; maximum 

 "breadth of zygospore 73-77 /^; niinininin breadth of 

 /ygosp. 50-6(5 [JL. 



ENGLAND. Esher West-end Common, and Wimble- 

 don Common (with /ygosp.), Surrey! 



Grot/r. Distfih/tfioii. Germany. Portugal. United 

 States. 



60. Closterium setaceum Ehrenb. 

 (PI. XXVI, figs. 9-13.) 



Closterium sctaceum Ehrenb. 1834 ; Infiis. 1838, p. 97, t. 0, f. ix ; Mene<?h. 



Synops. Desm. 1840, p. 235 ; Hass. Brit. Freshw. Alg. 1845, p. 373, t. 87, 



f/7 ; Ealf's, Brit. Desm. 1848, p. 17(5, t, 30, f. 4; Arch, in Pi-itch. Infus. 



1861, p. 750; Babenh. Flor. Enrop. Alo-ar. Ill, 1868, p. 136; Kiivlin. 



Al"-. Schles. 1878, p. 142 ; Wolle, Desm. U.S. 1884, p. 47, t. 8, f . 6, 7, - 1 1 ; 



( 'nuke, Brit, Desm. 188(5, p. :'. 1. t, 14, f. 4 ; Hanso-. Prodr. Al^rnfl. IJohin. 



1SSS, p. 184; De Toni, Syll. Ali^. 18S<), p. S5O : Eoy & Biss. Scott. Desm. 



IS'.ll, p. 219-. Nordst. Index Desm. 1896, p. 232; West & (>. S. West. 



Al-\ S. England, 1897, p. 482; Alga-fl. Yorks. 1900, p. 57; Al^. N. 



IreLin.l, 1902, p. 24. 



Cl. rnstratum Ehrenb. c. setaceum Klebs, Desm. Ostprenss. 1879, p. 18. 

 Arthrodia sctacea Ktintze, Revis. -en. plant, 1891, p. 884. 



Cells small, very slender, almost straight, 25-36 times 

 longer than their greatest diameter, median portion 

 of cell small, fusiform-lanceolate, both margins equally 

 convex, extremities prolonged into slender, setaceous, 

 colourless processes, which are slightly incurved and 

 obtuse at the apices ; each apical process is about 

 three-eighths the length of the cell ; cell-wall colourless 

 or pale straw-coloured, finely striated, about 13 fine 

 striations visible across the cell ; chloroplasts with 

 two pyrenoids; terminal vacnoles within the bas'e of the 

 apical processes, with three or four moving granules. 



Zygospores subquadrate or cruciform, with deeply 

 concave sides and truncate angles. 



Length 227-450 /x; breadth 7'5-12-5/i; breadth of 

 apices 0'7-1'5/x; breadth of zygosp. 30-32 p. 



