240 BKITISH DESMIDIACE^E. 



Geogr. Distribution. Sweden. Finland. India. Ceylon. 

 Siam. United States. 



This is one of the rarest of British Desmids. Its regularlv 



o </ 



undulate margins distinguish it from all other species of the 

 genus. 



Germs 25. DESMIDIUM Ag. 



Agardh, Syst. Alg. 1824, p. xv. 



Greville, Scott. Crypt, fl. 1828, vol. G, p. 38 ; in Hook, Brit. Fl. 1833; p. 402. 



Kiitz. Synops. Diat. 1834, p. 85 (sep.). 



Breb. Alg. Falaise, 1835, p. 53 (sep.). 



Menegh. Synops. Desm. 1840, p. 2 (sep.). 



Kail's in Ann. Mag. Nat. Hist, v. 9, 1842, p. 155 and 253. 



Kiitz. Phyc. generalis, 1843, p. 165. 



Hassall, Brit. Freshw. Alg. 1845, p. 341. 



Kiitz. Phyc. germ. 1845, p. 141. 



Ralfs, Brit, Desm. 1848, p. 60. 



Kiitz. Spec. Alg. 1849, p. 190. 



Nag. Gatt. eiiiz. Ala;. 1849, p. 130. 



De Bary, C'onj. 1858, p. 76. 



Wallich, Desm. low. Bengal, 1860, p. 186. 



Arch, in Pritch. Inf. 1861, p. 723. 



Rabenh. Krypt.-fl. Sachs. 1863, p. 180; Flor. Europ. Alg. 18G8, p. 153. 



Delp. Spec. Desm. subalp. 1873, p. 56. 



Nordst, Norges Desm. 1873. p. 49. 



Wood, Freshw. Alg. N. Amer. 1873, p. 126. 



Kirchn. Alg. Schles. 1878, p. 132. 



Gay, Monogr. loc. Conj. 1884, p. 44. 



Wolle, Desrn. U. S. 1884, p. 25. 



Cooke, Brit. Desm. 1887, p. 9. 



Hansg. Prodr. Alg. Bohm. 1888, p. 171. 



De Toni, Syll. Alg. 1889, p. 779. 



Wille in Engler, Naturl. Pflanzenf. 1890, p. 14. 



Turn. Freshw. Alg, E. India, 1893, p. 149. 



Comere, Desm. de France, 1901, p. 200. 



G. S. West, Brit. Freshw. Alg. 1904, p. 177. 



Didymoprium Kiitz. Phyc. generalis, 1843, p. 165 ; Phyc. germ. 1845, 



p. 141 ; Ralfs, Brit. Desm. 1848, p. 55 (in part) ; Kiitz. Spec. Alg. 1849, p. 



189 ; Arch, in Pritch. Inf. 1861, p. 723 (in part) ; Rabenh. Krypt.-fl. Sachs. 



1863, p. 180 ; Flor. Eur. Alg. 1868, p. 153 ; Delp. Spec. Desm. subalp. 



1873, p. 52 ; Wille in Engler, Naturl. Pflanzenf. 1890, p. 15 ; Turn. 



Freshw. Alg. E. India, 1893, p. 150 ; [= Subgenus Didymoprium Nordst. 



Norges Desm. 1873, p. 49 ; Gay, Monogr. loc. Conj. 1884, p. 44 ; Hansg. 



Prodr. Alg. Bohm. 1888, p. 172 ; De Toni, Syll. Alg. 1889, p. 783]. 

 Aptogonum Ehr. Inf. 1838, p. 382 ; Ralfs, Brit, Desm. 1848, p. 63 ; Wallich, 



Desm. low. Bengal, 1860, p. 191 ; Arch, in Pritch. Inf. 1861, p. 723 ; 



Rabenh. Flor. Eur. Alg. 1868, p. 155; Delp. Spec. Desm. subalp. 1873, 



p. 61 ; [= Submenus Aptogonum Nordst. Norges Desm. 1873, p. 50 ; 



Hansg. Prodr. Alg. Bohm, 1888, p. 171 ; De Toni, Syll. Alg. 1889, p. 781]. 



Cells united to form twisting filamentous colonies, 

 sometimes embedded in a thick mucous sheath ; cells 



