COSMOCLADIUM. 197 



constricted, sinus almost rectangular ; semicells subfusiform, 

 margins of semicell and angles provided with, simple or emarginate 

 spines ; with a circle of large granules round the base of the 

 semicell. 



Hob. Ireland : Carrantuohill, Cork. 



[Both St. tracliynotum West., and its var. annulatum are probably 

 forms of St. aculeatum (Ehr.) MenegJi.] 



EXCLUDED SPECIES. 



STAURASTRUM OSTEONUM West, ; Alg. X. Wales,' 1890, p. 293, 

 t. 5, f. 7. 



Genus 19. COSMOCLADIUM Breb. 1856. 



Breb. Liste Desm. 1856, p. 133. 



De Bary, Conj. 1858, p. 77. 



Arch, in Pritch. Infus. 1861, p. 752. 



Arch, in Quart. Journ. Micr. Sci. vol. 7, 1867, p. 299. 



Rabenh. Flor. Europ. Alg. 1868, p. 53. 



Kirchn. Alg. Schles. 1878, p. 105. 



Cooke, Brit. Desm. 1887, p. 78. 



De Toni, Syll. Alg. 1889, p. 804. 



\Ville, in Engler. Xaturl. Pflanzenfam. 1890, p. 11. 



Comere, Desm. de France, 1901, p. 180. 



G. S. West, Brit. Freshw. Alg. 1904, p. 173. 



Cells minute, constricted at the middle, usually com- 



i/ 



pressed and symmetrical in 3 planes at right angles to 

 each other; semicells subpyramidate, elliptic or sub- 

 reniform, cell- wall smooth ; chloroplasts axile, usually 

 one in each semicell, with a central pyrenoid and 4 

 projecting lobes; rarely with a single chloroplast in each 

 cell, the pyrenoid occupying a central position. Indi- 

 vidual cells indistinguishable from small species of 

 Cosmarium, united, however, to form colonies of greater 

 or smaller size (but never macroscopic), by means of 

 gelatinous threads, single or double, secreted through 

 pores in the cell membrane in the vicinity of the sinus. 

 Colonies branched in an irregular fashion, usually free 



d? / 



floating but sometimes of tree-like habit and attached 



o 



to other algae. 



Zygospores only known in one or two species, more or 



