COSMARIUM. 167 



Cells with the sinus more open, somewhat conical 

 with a subacute apex ; lower margins of semicells 

 convex, apices straight or very slightly retuse. Cell- 

 wall distinctly but minutely punctate. 



Length 17-19/>t; breadth 15-18/x; breadth of isth- 

 mus 3'5-4ju; thickness 7'5-8'5/x. 



ENGLAND. Putteiiham and Thursley Commons, 

 Surrey ! 



This variety comes nearest to C. bioculatum Breb. var. 

 excauatum Gutw. ; but is proportionately shorter, with a more 

 acute sinus, and the apices of the cells are straight or slightly 

 retuse. The cell-wall is also distinctly punctate. 



25. Cosmarium tenue Arch. 

 (Plate LXI, figs. 12-15.) 



Cosmarium tenue Arch, in Quart. Jonrii. Micr. Sci. 1868, p. 293 ; Cooke, 

 Brit. Desni. 1886, p. 92 ; West, Alg. W. Ireland, 1892, p. 147, t, 20, 

 f . 25 ; Johns. Bare Desni. U.S. I, 1894, p. 288 ; Nordst. Index Desm. 

 1896, p. 251 ; West & G. S. West, Alg. N. Ireland, 1902, p. 34. 



C. ellipsoideum Elfv. forma minor Anderss. Sverig. Chlor. 1890, p. 16, t. 1, 

 f. 9. 



Cells minute, about as long as broad, deeply con- 

 stricted, sinus linear, opening outwards ; semicells 

 transversely elliptic, apices slightly convex. Side view 

 of semicell circular. Vertical view elliptic, ratio of 

 axes about 1 : 1*8. Cell-wall smooth and colourless. 

 Chloroplasts axile, each with one pyrenoid. 



Zygospore globose and smooth. 



Length 14-16^; breadth 13'5-15-5^; breadth of 

 isthmus 3'5-4'5 p ; thickness 8'5 /n ; diam. zygosp. 

 22-23 fi. 



IRELAND.- -Lough Derryclare, and lakes E. of Lough 

 Bofin, Galway (with zygospores) ! Dublin and Wicklow 

 (Archer). Slieve Donard, Down! 



Geogr. Distribution- -Germany (form). Galicia in 

 Austria. Sweden. United States. 



C. tenue Arch, may very easily be confused with C. biocu- 

 latum Breb., but the semicells are more elliptic and the 

 zygospore is quite smooth. 



