70 BE1T1SH 



96. Cosmarium polygonum (Nag.) Arch. 

 (PI. LXXI, figs. 32-34.) 



(Cosmarium) polygonum Nitg\ Gfatt. einz. Alg. 18-19, p. 120, 

 t, 7 A, f 9. 



Cosmarium polygonum (Nag ) Arch, in Pritch. Infus. 1861, p. 732 ; Rabenh. 

 Flor. Europ. Alg-. Til, 1868, p. 167 ; Wolle, Desm. U.S. 1884, p. 65, 

 t. If), f. 30; West, Desm. Maine, 1888, p. 340 ; De Toni, Syll. Alg. 1889, 

 p. 949 ; Heimerl, Desm. alp. 1891, p. 600 ; Eoy & Biss. Scott. Desm. 

 1894, p. 171. 



Ursinella polygona Knntze, Revis. gen. plant. 1891, p. 925. 



? Cosmarium miiiutum Benn. Freshw. Alg. S. W. Surrey, 1892, p. 10, 

 t. 2, f. 11. 



Cells small, a little longer than broad, fairly deeply 

 constricted, sinus rather short and narrow ; semicells 

 broadly hexagonal, angles rounded, lateral ones very 

 slightly produced, sides faintly retuse (apex of semi- 

 cell sometimes straight). Side view of semicell 

 depressed-circular, slightly inflated at each side. 

 Vertical view subelliptic, with a prominent, somewhat 

 conical tumour at the middle of each side, ratio of 

 axes about 1 : 1'6. Cell-wall smooth or rarely finely 

 punctate. Chloroplasts axile with a central pyrenoid. 



Zygospore unknown. 



Length 15-21*5 p.; breadth 14-18*5 /x; breadth of 

 isthmus 3-7 /x; thickness 10-12'5 /x. 



SCOTLAND.- -Sutherland, Ross, Aberdeen, Kincardine, 

 Forfar, Argyll, Fife (Eoy $ Biswtt). 



IRELAND.- -Dublin and Wicklow (Archer). 



Geogr. Distribution.- -France. Germany. Sweden. 

 Burma. Madagascar. United States. 



The proportionately longer cells, the more pronounced 

 lateral angles, and the conical tumours of the vertical view 

 distinguish this species from C. abbrevidtum Racib. 



We have examined large forms of C. polygonum from 

 Maine, IT. S. A., up to 27 ju in breadth. One specimen of 

 C. polygonum var. exile West & G. S. West (' Welw. Afric. 

 Freshw. Alg./ 1897, p. 117), from W. Africa, was distinctly 

 stipitate, the stalk of attachment having its origin at one of 

 the lateral angles of a semicell and reaching a length of 

 32 IJL. This stalk was in no way gelatinous, but consisted of 

 cellulose, and was a continuous part of the cell-wall of the 

 specimen. Its diameter was about Oo /n. We have figured 

 this curious specimen on PL XCI, fig. 13. 



