132 BRITISH DESMIDIE.E. 



processes, which are shghtly forked at the apex and directed outwards ; but 

 in the front view seldom more than three or four processes are seen at once. 

 End view with three or four bipartite angles, their divisions divergent, subulate, 

 generally appearing acute at the apex, but sometimes, especially if looked at 

 obliquely, forked as in the front "^iew. 



Staiirastnim Iceve, in the front ^dew, agrees with S. brachiatum in its smooth 

 frond and forked divergent processes ; but the constriction at the middle is 

 greater, the processes are shorter, and if an angle be towards the eye its ge- 

 minate character will be detected without much difficulty. In the end view 

 this species is unlike any other. 



Length of frond ywo ^^ ^^ ^^^^ ' breadth -^^^j '■> breadth at constriction 

 •2^^ ; length of process from ^^3-5- to 3^. 



Tab. XXIII. fig. 10. «, 6, e. front views ; d. end view ; e. transverse view. 



******* Frond rough with puncta-like granules. 

 t End view with entire, rounded or truncate, angles or short rays. 

 20. S. alternans (Breb.) ; segments rough, narrow-oblong, and, from 

 their twisted position, unequal in the front view; end view wdth 

 the angles of one segment entire, and alternating with those of the 

 other. 



Staurastnim ^/•^co?•?^e, Ralfs, in Annals of Nat. Hist. v. 15. p. 141. t. 11. f. 2 

 (1845) ; Trans, of Bot. Soc. of Edinburgh, v. 2. p. 141. t. 14. Jenner, 

 Fl. of Tunbridge W^ells, p. 194. (Not of Meneghini according to Bre- 

 bisson.) 



Goniocystis {Trigonoeystis) hexaceros, Hassall, Brit. Freshwater Algoe, p. 352 

 (1845). 



Staurastnim alternans, Brebisson, in lit cum icone (1846). 



Dolgelley and Penzance, J. R. Barmouth, Rev. T. Salwey. Weston Bogs 

 near Southampton ; and several stations in Sussex, Surrey and Kent, Mr. 

 Jenner. Near Bristol, Mr. Thivaites. Glen Lin, Aberdeenshire (alt. 1300 

 feet). Dr. Dickie. Near Aberdeen, 3Ir. P. Grant. Ambleside, Mr. Side- 

 botham. 



Falaise, Brebisson. West Point, New York, Bailey. 



Frond rough with minute pearly granules, which, except on the margin, 

 appear like puncta ; segments two or three times longer than broad, oblong, 

 twisted, so that in the front view one of them appears shorter on one side, in 

 consequence of the blending together of two of the angles. The end view is 

 triangulai', with concave sides and very obtuse entire angles. The angles of 

 the lower segment are seen alternating with those of the upper. 



I formerly described this plant as the Staurastnim tricorne, but that species 

 in the front view is prolonged at the sides into short processes ; I am not certain 

 that the two are distinct, but in doubtful points I think it right to defer to 

 M. de Brebisson' s opinion. 



Staurastrum alternans may be known from S. dilatatum and S. punctii- 

 latiim by its unequal segments in the front view and alternating angles in the 

 end one. 



