166 BRITISH DESMIDIACEJE. 



lateral margins slightly convex, apex strongly convex, 

 lateral angles upwardly turned and markedly mamil- 

 late, each mamilla with two ill-defined rings of minute 

 grannies, few grannies in each ring. Vertical view 

 triangular, sides very faintly convex, angles slightly 

 produced and submamillate, with two rings of minute 

 granules. 



Zygospore globose, furnished with long, slender 

 spines, the apices of which are deeply 2 4-furcate, 

 with the divisions widely spreading. 



Length 30-84 fi; breadth 29-32-5 /u,; breadth of 

 isthmus 10*5-11 '5 p.; diam. zygosp. without spines 

 31 /A, with spines 63 ^ ; length of spines 15-19 ^. 



ENGLAND.- -Thursley Common, Surrey (with zygo- 

 spore) ! 



Only one zygospore of this species lias been observed and 

 it was at first referred to St. corniculatum Lund. (cf. W. & 

 Gr. S. West, ' New and Int. Fresliw. Alg/ 1896 ; p. 157, t. 4, 

 f. 37). At that time the existence of St. tracliytithophorum 

 was not known, and we failed to notice the granules on the 

 mamillate angles of the semicells still attached to the zygo- 

 spore. The discovery of vegetative cells of St. trachytitho- 

 pliorum led to the re-examination of the supposed zygospore 

 of St. corniculatum, when it was at once seen that old 

 semioells did not belong to that species but were those of 

 St. tracJiijtithophoruin . 



28. Staurastrum botrophilum "Wolle. 

 (PI. CXXVI, fig. 4.) 



Staurastrum lotrophilum Wolle in Bull. Torr. Bot. Club, 1881, p. 2, t. 6, 

 f. 13; Wolle, Desm. U. S. 1884, p. 131, t. 42, f. 11, 12 'figures poor; 

 fig. 13 ?" ; De Toiii, Syll. Alg. 1889, p. 1170 ; Eoy & Biss/ Scott. Desm. 

 1893, p. 18 (sep.) ; W*. & O. S. West, SomeN . Amer. Desm. 1896, p. 261 ; 

 Cushman in Ehodora, vii, 1905, p. 262. 



Cells of medium size, 1-glJ times as long as broad, 

 very deeply constricted, sinus narrowly linear with a 

 slightly dilated extremity; semicells pyramidate -trun- 

 cate, angles a little rounded, sides subconvex, apex 

 truncate and straight. Vertical view triangular, sides 

 faintly retuse in the middle, angles acutely rounded 



