8 BRITISH DESMIDIACE.E. 



rarely elliptical, dorsal and lateral margins nearly 

 straight or very slightly convex ; with a long spine at 

 each angle ; spines usually somewhat diverging, some- 

 times parallel, and very rarely converging. Vertical 

 view triangular, rarely quadrangular, lateral margins 

 slightly concave, angles slightly turgid and terminated 

 by a strong spine. Chloroplast axile with a central 

 pyrenoid and two lobes projecting into each angle. 



Zygospore spherical, with a number of rather short, 

 stout spines, broad at their base. 



Length, not including the spines, 18-27^ ; breadth, 

 not including the spines, 17-27 (JL ; breadth of isthmus 

 5-8 (JL ; length of spines 3-8 [JL ; diam. zygosp., without 

 spines, 32'5 (JL ; length of spines, 5-10 [JL. 



ENGLAND. Cumberland ! Westmoreland ! Lanca- 

 shire (Rolfs}. W., N., and E. Yorks! Essex! Warwicks 

 (Wills). Surrey ! Sussex ! Kent (Rolfs). Hants ! 

 Wilts ! Devon ! (Harris). Cornwall ! Plankton of 

 Ennerdale Water, Cumberland, and of Hawes Water 

 and Stickle Tarn, Westmoreland ! 



WALES. Capel Curig (Cooke & Wills), Llyn Idwal, 

 Llyn Ogwen, Llyn C4eirionedd, Llyn Bodgynwydd and 

 Y Foel Eras, Carnarvonshire ! In the plankton. 



SCOTLAND. General : zygospores not uncommon (Roy 

 & Biss.). Bute ! Loch Doon, Ayrshire ! Wigtownshire ! 

 Lewis and Harris, Outer Hebrides ! General in the 

 plankton ! 



IRELAND. Donegal ! Mayo and Clare Island ! Gal- 

 way ! Kerry ! Dublin and Wicklow (Arch.). London- 

 derry ! In the plankton ! 



Geogr. Distribution. France. Germany. Switzerland. 

 Austria and Galicia. Hungary. Servia. Italy. Norway. 

 Finmark. Sweden. Poland. N., Central and S. Russia. 

 Faeroes. Iceland (var.). Greenland. Siberia. Mongolia. 

 Central China. Japan. India. Ceylon. Australia. New 

 Zealand (var.). E. Africa. Alaska. LTnited States. 

 Canada. Colombia. 



St. dejectum is an extremely common and widely distributed 



