OOCARDIUM. 203 



Zygospore recorded by Gronblad (' Desm. Keuru,' 1920, 

 p. 82), but without description or figure. 



Length 22-27 pi ; breadth 18-20 p ; thickness 12-15 EJL; 

 breadth of isthmus 3 '5-7 pi. 



ENGLAND.--? Thursley Common, Surrey (identified 

 with doubt) ! 



WALES. Capel Curig ! arid pool near Llyn Elsie, 

 Bettws-y-coed (Arch.), Carnarvonshire ! In the plankton ! 



SCOTLAND. --Dalbrake and Heughhead in Sfcrachan, 

 Kincardine (Roy & Biss.). Near Tarbert, Harris, Outer 

 Hebrides ! 



IRELAND.- -Dublin ; Carrick Mts., Wicklow ; Callery 

 Bog (Arch.). In the plankton ! 



Geoqr. Distribution. Germany. Austria. Norway. 



U / i 



Finland. United States. 



Both Schroder and Liitkemliller have carefully investigated 

 this species, and found that each cell possesses 4 special groups 

 of pores near the isthmus which are responsible for the secretion 

 of the gelatinous connecting threads (cf. PL CLVIII, fig. 16). 

 These pores are seen in the basal view of the semicell lying at 

 opposite poles of the aperture which represents the isthmus. The 

 connecting threads appear early during cell division and are seen 

 as delicate strands stretching between the older semicells, 

 becoming longer and stronger as the cells reach maturity. They 

 very often show somewhat fusiform thickenings between each 

 pair of cells, the significance of which is not properly understood. 



Genus 20. OOCARDIUM Nag. 1849. 



Nag. Gatt. einz. Alg. 1849, p. 74. 



Kiitz. Spec. Alg. 1849, p. 196. 



Kiitz. Tab. Phye. II, 1850, t. 83, f. 5. 



Pxabenh. Flor. Eur. Alg. 1868, pp. 13, 53. 



De Toni, Syll. Alg. 1889, p. 658. 



Senn in Botan. Zeitung, 1899, p. 81. 



G. S. West, Brit. Freshw. Alg. 1904, p. 174. 



Cells essentially of the Cosmarium type, small, de- 

 pressed, considerably broader than long, very slightly 

 constricted, unequally flattened on the two sides, so 

 that the cells are only symmetrical in 2 planes at right 

 angles instead of 3, as is general in Cosmarium and the 



