40 BRITISH DESMIDIACE^. 



present position, the writer is inclined to attribute the figure to 

 St. denticulatuni. 



68. Staurastrum Avicula Breb. 

 (PI. CXXXIII, figs. 8-10 and 12.) 



Staimistruin Avicula Breb. in Ralfs, Brit. Desm. 1848, p. 140, t. 23, f. 11 ; 

 Arch, in Pritch. Infus. 1861, p. 738, t. 3, f. 18, 19 ; Rabenh. Flor. Europ. 

 Alg. 1868, p. 204 ; Lund. Desm. Suec. 1871, p. 61 : Delp. Desm. sulalp. 

 1877, p. 165, t. 12, f. 22-29 ; Turn. Alg. Strensall Common, 1883, p. 80, 

 t, 1, f. 1 ; Wolle, Desm. U. S. 1884, p. 123, t. 40, f. 30-32 ; Cooke, Brit. 

 Desm. 1887, p. 145, t. 50, f . 9 ; De Toni, Syll. Alg. 1889, p. 1153 ; West, 

 Ale. W. Ireland, 1892, p. 174; Roy & Biss. Scott, Desm. 1893, p. 17, 

 t. 3, f. 11 ; West & G. S. West, Alg. S. England, 1897, p. 493 ; G. S. West, 

 Alga-fl. Camb. 1899, p. 25, t. 396, f. 10 ; West & G. S. West, Alga-fl. 

 Yorks. 1902, p. 97; Alg. N. Ireland, 1902, p. 46; Borge in Botan. 

 Notiser 1913, p. 29 ; Gronblad, Desm. Keuru, 1920, p. 57, t. 3, f. 36-38. 



Cells small, about as long as broad, deeply constricted, 

 sinus variable, usually linear for some little distance, 

 then opening widely ; semicells subelliptical or sub- 

 triangular, dorsal margin slightly convex, lateral mar- 

 gins sometimes nearly straight, but often very convex ; 

 upper angles of semicells furnished with two minute 

 spines, one placed vertically above the other, the dorsal 

 one often slightly longer ; cell-wall more or less dis- 

 tinctly rough with minute granules arranged in con- 

 centric rows round the angles. Vertical view triangular, 

 sides concave, angles very obtuse, one spine only being 

 visible, as a rule, at each angle. 



Zygospore not very well known, but according to 

 Roy, probably globose and furnished with a number of 

 conical spines, very broad at the base and bifurcate at 

 the apex. 



Length 29-34*5 ^ ; breadth, with spines, 35 u ; breadth 

 of isthmus 9-1 1 JJL . 



ENGLAND.- -Westmoreland ! (Biss.). W., N., and E. 

 Yorks ! Leicester (Roy). Cambs ! Plankton of Bracebridge 

 Pool, Warwicks ! Worcs ! Hants ! (Bennett). Devon ! 

 (Harris). Cornwall ! 



WALES. Capel Curig (Cooke & Wills) I Llyn Ogwen 

 and Llyn Bodgynwydd, Carnarvonshire ! Ffestiniog, 

 Merioneth ! 



