STAURASTRUM. 29 



margins convex, apex of semicells truncate or slightly 

 retuse, angles produced to form a colourless recurved 

 spine ; cell-wall finely granulate-denticulate. Vertical 

 view triangular, angles slightly inflated and ending in 

 a short straight spine ; lateral margins gently concave. 



Zygospore unknown. 



Length 19-30fji ; breadth, not including spines, about 

 19-24fjt; length of spines 6 JJL ; breadth of isthmus 

 7-10 p. 



ENGLAND. Puttenham Common. Surrey ! 



s t 



Geogr. Distribution. Germany. Galicia in Austria. 

 Sweden. N. Russia. 



St. tunguscanum is closely allied to St. granulosum (Ehr.) 

 Ealfs and St. lunatum Ralfs. It differs from both these specie 

 in its distinctly truncate or retuse apex, and its angular spines 

 are also very much stouter than the delicate spines of St. granu- 

 losum. 



59. Staurastrum lunatum Ealfs. 

 (PL CXXXIII, figs. 17-19.) 



Staurastrum lunatum Ralfs, Brit. Desm. 1848, p. 124. t. -'54, f. 12 ; Arch, in 

 Priteh. Inf. 1861, p. 738 ; Rabenh. Krypt. F!. Sachs. 1S63, p. 193 ; Flor. 

 Europ. Alg. 1868, p. 221 ; Cooke, Brit. Desm. 1887, p. 143, t, 50, f. 5; 

 De Toni, Syll. Alg. 1889, p. 1146; Racib. Desm. Xmve, 1889, p. 28; 

 West, Add.' Alg. W. Yorks. II, 1891, p. 247 ; Alir. \V. Ireland, 1892, 

 p. 173 ; Roy & Biss. Scott. Desm. 1894, p. 22 : West & G. 8. West, Alg. 

 S. England,' 1897, p. 493; Schroder, Gallertbildimu Ah,'. 1902, p. 168, 

 t. 7, f. 16; Teodoresco, Mater, flor. alg. Rouman. l!i<>7. p. 184. 



Cells rather under medium size, about as long as 

 broad or a little shorter, not counting the spines, deeply 

 constricted, sinus acute and widening outwards ; semi- 

 cells semicircular or almost lunate, directed away from 

 each other, dorsal margin very slightly convex, ventral 

 margin very tumid, upper angles of semicell obtuse, 

 and ending in a short stout spine which projects obliquely 

 outwards. Cell- wall uniformly rough with tiny granules 

 arranged in concentric rows round the angles. Vertical 

 view triangular, sides concave, angles terminating in a 

 short spine, granules becoming smaller towards the 



