BRITISH DESMIDIACE.E. 



Genus 13. EUASTRUM Ehrenb., 1832. 



Ehrenb. Entwick. Lebends. d. Infus. 1S32, p. 82 (in part). 



Ehrenb. Infus. 1838, p. 160. 



Ealfs in Ann. Mag. Xat. Hist. 1844, p. 187. 



Ealfs, Brit. Desin. 1848, p. 78. 



De Baiy, Conj. 1858, p. 50, 70-71. 



Arch, in Pritch. Infus. 1861, pp. 720, 728. 



Eabenh. Flor. Europ. Algar. Ill, 1868, p. 179. 



Wolle, Desm. U.S. 1884, p. 97. 



Cooke, Brit. Desin. 1886, p. 63. 



Hansg. Prodr. Algenfl. Bohm. 1888, p. 203. 



De Toni, Syll. Alg. 1889, p. 1065. 



G. S. West, Treatise Brit. Freshw. Alg. 1904, p. 164. 



Cells of variable size, longer than broad, compressed, 

 deeply constricted in the middle, sinus generally linear 

 (rarely open) ; semicells commonly truncate-pyramidate, 

 apex with a median incision of variable depth, sometimes 

 scarcely evident or absent, lateral mar sins entire, 



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sinuate, or variously lobed, at or near the centre of the 

 semicells v:ith one or more somewhat hemispherical pro- 

 tuberances (or tumours) variously disposed; vertical 

 view more or less elliptical, with one or more pro- 

 tuberances on each side ; one chloroplast in each semi- 

 cell, often irregularly lobed and ridded, with a sinsrle 



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central pyrenoid in the small species, and a number of 

 scattered ones in the large species. 



Zygospores globose, ellipsoid, or oblong-ellipsoid, 

 ornamented with numerous conical papillae, or with 

 simple (or furcate) spines. 



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