76 BRITISH DESMIDIACE^B. 



This species is on the border-line between the genera 

 Euastrum and Cosmarium, but we are inclined to retain it in 

 the former genus on account of the distinctly emarginate 

 apices. 



It has two near relatives in Cosmarium subbinale (Nordst.) 

 Lagerh. and C. miedzyrzecense Eichl. & Gutw., neither of 

 which are known to occur in Britain. 



NOTE. In his 'Freshw. Alg. Eng. Lake Distr./ 1886, 

 Bennett figures very roughly a Desmid which he terms 

 " Euastrum crenatum Kiitz/ 5 His short description and his 

 outlined figure do not agree, however, with Kiitzing's descrip- 

 tion of E. crenatum. What Bennett's plant was we do not 

 know, neither is the information he gives concerning it of 

 sufficient value to establish a species. It seems to us that 

 it might possibly be a form of Cosmarium tetragonum Nag. 



Genus 14. MICRASTERIAS Ag., 1827. 



Ag. in Flora, 1827, p. 642. 



Menegh. Synops. Desm. 1840, p. 214. 



Ralfs, in Ann. Nat. Hist. 1844, p. 259. 



Hass. Brit. Freshw. Alg. 1845, p. 385. 



Ralfs, Brit. Desm. 1848, p. 68. 



De Bary, Conj. 1858, pp. 39, 40, 47, 50, 70. 



Arch, in Pritch. Infus. 1861, pp. 720, 725. 



Rabenh. Flor. Etirop. Alg. Ill, 1868, p. 187. 



Wolle, Desm. U.S. 1884, p. 108. < 



Cooke, Brit. Desm. 1886, p. 53. 



Hansg. Prodr. Algenfl. Bohm. 1888, p. 207. 



De Toni, Syll. Alg. 1889, p. 1109. 



(jr. S. West, Treatise Brit. Freshw. Alg., 1904, p. 165. 



Cells of variable size, often large, usually a little 

 longer than broad, sometimes subcircular in general 

 outline, usually much compressed, very deeply con- 

 stricted in the middle, sinus usually linear (open 

 outwards in several species) ; semicells subsemicircular, 

 usually five-lobed (in some species three-lobed) ; polar 

 lobe generally widely cuneate, emarginate, or widely 

 notched ; lateral lobes usually bilobulate, lobules 

 generally slightly bilobed ; median part of base of 

 semicells generally without protuberances ; vertical 

 view elliptic-lanceolate or linear-lanceolate ; one lobed 

 chloroplast in each semicell, with many scattered 

 pyrenoids. 



