DESMIDIUM. 243 



often long and twisted, usually destitute of a gelatinous 

 sheath. 



Zygospores large, smooth and subspherical, produced 

 after the partial or total dissociation of the filaments 

 into individual cells. 



Length 13-18 ( u : breadth 26-30 u ; breadth of 

 isthmus 21-24 UL; breadth of apices 21-24 pt; diam. 

 zyo-osp. 18-26tJL. 



ENGLAND. Ambleside (Kalfs), Loughrigg !, Scan- 

 dale !, Bowness ! (Bissett) and in the plankton of 

 Windermere !, Westmoreland. Strensall (W. B. Turn.), 

 and Pilmoor !, X. Yorks. 



WALES. Capel Curig ! (Cooke & Wills), Llyn Padarn!, 

 Llyn Idwal !, and in the plankton !, Carnarvonshire. 

 Llyn Coron. Anglesey ! Dolgelly. Merioneth (Rolfs}. 



SCOTLAND.- Xot common ; Sutherland !, Aberdeen, 

 Kincardine. Forfar, Perth, Argyle and Fife (Roy & 

 Biss.). Plank- ton of Loch Ruar, Sutherland !, Lochs 

 Cuthaig and Fadaghoda, Lewis !, Loch Laxadale, Harris !, 

 and Loch Nan Kun. N. Uist. Outer Hebrides ! 



IRELAND.- -Ball ynahinch, and Roundstone, Galway ! 



Geocjr. Distribution. -France. Germany. Switzer- 

 land. Galicia and Austria. Turkey. Italy. Norway. 

 Sweden. Denmark. Finland. Japan. India. Ceylon. 

 Burma. Java. Australia. Madagascar. Sandwich 

 Isles. United States. Brazil. Ecuador. Colombia. 



D. Aptogonum is readily distinguished from all other British 

 species by the large and distinct spaces between adjacent cells. 

 It is not at all common, but occurs in plenty in the bogs near 

 Capel Curig Lake, Carnarvonshire. 



Var. Ehrenbergii Kiitz. (PL CLXIV, figs. 4, 5.) 



Odontella Desmidlum Ehr. Inf. 1838, p. 153. t. 16, f. iv. 



Aptogonum Desmidlum var. ft Ralfs, Brit. Desm. 1848, p. 64, t. 32, f. 1, 



e-h. 

 Desmidlum Aptogonum var. Ehrenbergii Kiitz. Spec. Alg. 1849, p. 190 ; 



Rabenh. Flor. Europ. Alg. 1868, p. 154 ; Hansgirg, Prod. Alg. Bohrn. 



1888, p. 172; De Toni, Syll. Alg. 1889, p. 781 ; West & G. S. West, Some 



N. Amer. Desm. 1896, p. 233, t. 12, f. 23 ; Alga-fl. Yorks. 1902, p. 110. 

 Aptogonum diagonum Delp. Spec. Desm. subalp. 1873, p. 64, t. 3, f. 6-10. 



