118 BRITISH DESMIDIACE^. 



Genus 18. STAURASTRUM Meyen, 1829; em. Ralfs. 



Meyen in Nova acta Acad. Csesar. Leop. Carol. Nat. cur. t. 14, 1828 (1829). 



[Description very imperfect.] 

 Ehrenb. Infus. 1838, p. 142. 

 Kiitz. Phyc. gener. 1843, p. 163. 

 Half's in Ann. Mag. Nat. Hist, xv, 1845, p. 149. 

 Ealfs, Brit. Desm. 1848, p. 119. 

 Arch, in Pritch. Infus. 1861, pp. 720, 737. 

 Eabenh. Flor. Europ. Alg. Ill, 1868, p. 196. 

 Lund. Desm. Suec. 1871, p. 7. 

 Delp. Desm. subalp. 1873, p. 38. 

 Kirchn. Alg. Schles. 1878, p. 163. 

 Wolle, Desm. U. S. 1884, p. 119. 

 Cooke, Brit. Desm. 1887, p. 138. 

 Hansg. Prodr. Algenfl. Bohm. 1888, p. 210. 

 De Toni, Syll. Alg. 1889, p. 1136. 

 Turner, Freshw. Alg. E. India, 1893, p. 132. 

 G. S. West, Treatise Brit. Freshw. Algse, 1904, p. 171. 

 Wille in Engler & Prantl, Natiirlich. Pflanzenfam. 1909, p. 9. 

 Didymocladon Ealfs, Brit. Desm. 1848, p. 144; Delp. Desm. subalp. 1877, 



p. 78 (sep. p. 174). 

 Pleurenterium (Lund.) Wille in Engler & Prantl, Natiirlich. Pflanzenfam. 



1890, p. 11 [= Subgen. Pleurenterium Lund. Desm. Suec. 1871, p. 72]. 

 Tempered Bougon in Le Micrographe preparateur, iv, 1896, p. 210. 



Cells of very variable size, generally longer than 

 broad (excluding spines or processes), usually with a 

 radial symmetry; median constriction variable in 

 depth ; semicells most variable in outline, subcircular, 

 elliptic, subtriangular, campanulate, trapeziform, etc., 

 with the angles frequently produced into hollow processes 

 of variable length ; vertical view 3-5 (or even up toll) 

 -angular or -radiate (rarely compressed). Cell-wall 

 smooth, punctate, scrobiculate, or granulate, or clothed 

 with spines of various kinds; sometimes furnished 

 with flattened, emarginate, or spiny verrucas. Chloro- 

 plasts generally axile, one in each semicell, consisting 

 of a central mass containing one pyrenoid from which 

 lobes radiate into the angles or processes ; in a few 

 species sometimes parietal or partially so (often most 

 irregular) and sometimes axile, and containing several 

 pyrenoids. 



Zygospores globose or angular, rarely winged or 

 furnished with blunt warts, commonly clothed with 

 long spines, which are simple or furcate at their 



