254 BRITISH DESMIDIACE^:. 



SCOTLAND.- -Plankton of Loch nan Eun, N. Uist, and 

 Loch Fadaghoda, Lewis, Outer Hebrides ! 



Geogr. Distribution.- -India, Ceylon. New Zealand. 

 United States. Brazil. 



8. Desmidium quadratum Nordst. 

 (PL CLXVI, figs. 6, 7.) 



Desmidium (Didymoprium) quadratum Nordst. Norges Desm. 1873, p. 49, 



t. 1, f. 24. 

 I), quadratum Arch, in Journ. Bot, 1874, p. 92 ; Wolle, Desm. U. S. 1884, 



p. 26, t. 49, f. 5 ; Lagerh. Bidr. Amer. Desm.-fl. 1885, p. 227, t. 27, f. 1 ; 



De Toni, Syll. Alg. 1889, p. 784 ; Roy & Biss. Scott. Desm. 1893, p. 9 ; 



W. & G. S.'West, Some N. Amer. Desm. 1896, p. 233, t. 12, f. 25 ; Desm. 



U. S. 1898, p. 321 ; Alg. Ceylon, 1902, p. 194 (forma) ; G. S. West, Brit, 



Freshw. Alg. 1904, p. 177, f. 69 B ; Fritch, Alg. Ceylon, 1907, p. 245, 



f. 4 F ; Bernard, Alg. unicell. domaine Malais, 1909, p. 19, t, 1, f. 12. 

 Didymoprium quadratum Racib. Nonn. Desm. Polon. 1885, p. 11. 



Filaments nearly cylindrical, twisted ; cells about Ij 

 times broader than long, slightly constricted, with a 

 shallow linear sinus, semicells short, pyramidate-truncate, 

 lateral margins biundulate. basal angles acutely rounded ; 

 apex rather broad and truncate ; side view of semi- 

 cell quadrangular with scarcely any trace of a median 

 constriction. Vertical view subcircular with 2 opposite 

 mamillse. Chloroplasts axile, one in each semicell 

 with a central pyrenoid and 6 or 7 radiating plates. 



Zygospore globose or subglobose, with a thick, smooth 

 membrane. 



Length 19-20 \L ; breadth 25 \L ; breadth of apex 

 12'5pt ; thickness 19-20^ ; diam. zygosp. 24-28 [/.. 



SCOTLAND.- -Very rare : Slewdrum in Birse, Aberdeen 

 (Roy & Biss.). 



Geogr. Distribution. Galicia in Austria. Norway. 

 Sweden. Poland. Afghanistan. Ceylon. United 

 States. Guiana. Brazil. 



This species is very similar in form to the preceding one, 

 except that it is relatively broader. The zy go spores of the two 

 species are, however, quite different. 



Genus 26. GYMNOZYGA Ehren. 1841. 



Ehrenb. in Berlin Monatsb, 1841, p. 212 (with description only of G. monili- 

 formis). 



