210 I5UITISH DESMTTHACK.y.. 



Genus 12. Tetmemorus Ralfs, 1844. 



Ralfs' iu Ann. Mag. Nat. Hist. 1844, p. 25<>. 



Hassall, Brit. Freshw. Alg. 1845, p. 377. 



I, 1 ,- 1 Us, Brit. Desm. 1848, p. 145. 



An-li. in Pritch. Infus. 1861, p. 720 and 7411. 



Kalicnh. Hor. Enrop. Algar. Ill, 18<>s, p. i:;:i 



Cooke, Brit. Desm. 188(i, p. 48. 



DC Toni, Syll. Alg. 1889, p. 8(ii;. 



Cells elongated, straight, cylindrical or fusiform- 

 cylindrical, a little compressed at each apex, slight I v 

 constricted in the middle, with a very narrow incision 

 in the middle of each apex, apical angles rounded; 

 vertical view circular or broadly elliptical; cell-wall 

 minutely scrobiculate, or punctate ; with a single 

 chloroplast in each semicell, containing a central row 

 of pyrenoids. 



This genus is easily distinguished from Pleurot&nium by 

 I he well-marked apicsil incisions, and by other minor cha- 

 racters. It differs from Closterium in its straight cells, its 

 median constriction, and in its broad apices with median 

 incisions. From Penium it is distinguished by its more 

 evident median constriction and its apical incisions ; from 

 some Penia it is also at once separated by its method of 

 division and the absence of periodical growth. 



It is closely connected with Euastrum through the American 

 Drsmid Euastrum giganteum (Wood) Nordst., formerly de- 

 scribed by Wood as Tetmemurus giganteus. 



The nearest genus to it in the general form of the cells is 

 the African and S. American genus Ichthyocercus. 



1. Tetmemorus Brebissonii (Menegh.) Ralfs. 

 (PL XXXII, figs. 1, 2.) 



lirebissonii Menegh. Synops. Desui. 1840, p. 236. 



Hi-i'bissonii (Menegh.) Kalfs, in Ann. Mag. Nat, Hist. 1M 4, 

 p. 2.Y7, 1 . 8, f. 1 ; Haas. Brit. Freshw. Alg. 1845, p. 377, t. 89, f . 5 ; Ealfs, Bi-il . 

 IVsm. 1848, p. 145, t. 24, f. 1 </, b, c; De Bary, Conj. 1858, p.*73 ; Airli. 

 in Pritch. Infus. 1801, p. 74G,t. 2,f. 11-13 ; Kabt-nh. Flor. Europ. Algar. 

 HI, 1868, p. 139 ; Kirchn. Alg. Schk-s. 1878, p. 145 ; Wolle, Desm. U.S. 

 1884, p. 91, t. 20, f. 1, 2; t. 5<), f. HI! ; Cookc, Brit. Desm. 188(3, p. 48, t. 18, 

 f. 7; Hansg. Prodr. Algenfl. IJulim. 1888, p. 188; De Toni, Syll. Alg. 

 ISM), p. 8(iG; West, Alg. W. Ireland, 1892, p. 131; Eoy & Biss. Scott. 

 Desm. 1894, p. 242; Nordst. Index Desm. 1896, p. 68; West & G. S. 

 West, Alg. S. England, 1897, p. 483 ; Alga-fl. Yorks. 1900, p. 59; Alg. 

 N. Ireland, 1902, p. 26. 



