110 BRITISH DESMIDIACE^E. 



brachycerum. It is readily distinguished from the latter species 

 by its longer and more slender processes, which are not so 

 strongly incurved. The ' body ' of the cell is also relatively 

 smaller, and not as broad in proportion with the length of cell. 



115. Staurastrum crenulatum (Nag.) Delp. 

 (PL CXLIII, figs. 9-13.) 



Phycastrum (Stenactinium) crenulatum Nag. Gatt. einz. Algen, 1849, p. 129, 



t. 8 B, a. 

 Staurastrum crenulatum Delp. Spec. Desm. subalp. 1877, p. 164, t. 12, 



f. 1-11 ; Wolle, Desm. U. S. 1884, p. 126, t. 42, f. 26-29 ; Schmidle, Beitr. 



Alp. Alg. 1895, p. 36 ; G. S. West, Variation Desm. 1899, p. 393, t. 11, f. 



21-27 ; Borg. Alg. Faeroes, 1901, p. 234, t. 7, f. 16 ; Cushman in Bull. 



Torr. Bot. Club, 30, 1903, p. 564; Teodor. Mater, flor. alg. Rouman. 



1907, p. 185. 



Cells small, about as long as broad, sometimes a little 

 longer or shorter according to the relative length of the 

 processes, constriction deep, sinus acute, nearly rect- 

 angular, often minutely acuminate at the apex ; semi- 

 cells broadly oval or subfusiform, apex broad, truncate 

 or slightly convex, and often somewhat elevated, 

 sometimes with a pair of verruca? ; ventral margin very 

 tumid ; semicells gradually attenuated bo form hori- 

 zontal processes of varying length, with more or less 

 denticulate undulate margins, denticulations near the 

 apex of the semicell often tending to become emar- 

 ginate. Vertical view 3-5-angular, sides concave, with 

 a pair of emarginate verrucse just within the margin ; 

 angles produced to form denticulate processes. 



Zygospore unknown. 



Length 20-25 \L ; breadth, including the processes, 

 20-33 u. ; breadth of isthmus 5-7 \L. 



ENGLAND. --Roundhay Park, Leeds, and Cautley 

 Spout, W. Yorks ! Pilmoor and Stokeley, N. Yorks ! 

 Dernford Fen, Cambs ! Burnham Beeches, Bucks ! 

 Near Goring, Oxford ! Warwicks ! and in the plankton 

 of Bracebridge Pool, Button Park! Worcester ! (Griffiths). 

 Uxbridge, Middlesex ! Tliursley Common, Surrey ! 



WALES. Capel Curig, Carnarvonshire (Roy). 



SCOTLAND. Pretty common (Roy & Biss.). Orkneys ! 



