EUASTRI'M. 27 



The basal view of tlie semicell given by Halt's (I.e. t. 32, 

 f. ob) is incorrect. We have examined hundreds of specimens 

 of this species and the vertical view is broadly elliptic, 

 occasionally exhibiting' the merest trace of three undulations 

 along each side. 



14. Euastrum ansatum Ralfs. 

 (PI. XXXVI, figs. 10-13.) 



': E vast rum circulare Hass. Brit. Freshw. Alg. 1845, p. 383, t. 90, f. 5 



(figure bad) ; Ralfs, Brit. Desm. 1848, p. 85, t. 14, f. 3 a (from Hassall) ; 



Arch, in Pritch. Infus. 1861, p. 729; Cooke, Brit. Desm. 1886, p. 71. 



t. 34, f. 2 (from Hassall or Ralfs) ; De Toni, Syll. Alg. 1889, p. 1097 ; 



West, Alg. W. Ireland, 1892, p. 138 ; Alg. Eng/Lake Distr. 1892, p. 723. 

 E. ansatum Ralfs, Brit. Desm. 1848, p. 85, t. 14, f. 2 [Not E. ansatum 



Ehrenb., 1832, which is Cosmarium ansatum (Ehrenb.) Rabenh.1 : Arch. 



in Pritch. Infus. 1861, p. 729 ; Lund. Desm. Suec. 1871, p. 20 ; "Kirclm. 



Alg. Schles. 1878, p. 158 ; Cooke, Brit. Desm. 1886, p. 70, t. 33, f . 5 ; 



Hansg. Prodr. Algenfl. Bohm. 1888, p. 206 ; De Toni, Syll. Alg. 1889, 



p. 1096; West, Alg. W. Ireland, 1&92, p. 138; Roy A: Biss. Scott. Desm. 



1893, p. 176; Nordst. Index Desm. 1896, p. 46;* West & G. S. West, 



Alg. S. England, 1897, p. 483; Alga-fl. Yorks. 1900, p. 62; Alg. N. 



Ireland, 1902, p. 28 ; Scott. Freshw. Plankton, I, 1903, p. 525. 

 Cosmarium circulare Kiitz. Spec. Alg. 1849, p. 174. 

 Euastrum circulare D. Hassallii Breb. Liste Desm. 1856, p. 122. 

 Didymidium (Euastrum) ansatum Reinsch, Algenfl. Fraiiken, 1867, p. 130. 

 Euastrum Ral/sii Rabenh. Flor. Europ. Algar. Ill, 1868, p. 184. 

 E. ansatum var. sublobatum Delp. Desm. subalp. 1873, p. 103, t. 6, f. 35-36. 

 Helierella circularis Kuntze, Revis. gen. plant, 1891, p. 898. 

 H. ansata Kuntze, I.e. 



Cells somewhat small, about twice as long as broad, 

 deeply constricted, sinus narrowly linear with a dilated 

 extremity ; semicells pyramidate with a broad base, 

 basal angles rounded, lower part of lateral margins 

 convex with a slight undulation above the basal angles, 

 upper part of margins concave, apex rotundo-truncate, 

 with a narrow and fairly deep median incision; semi- 

 cells with a slight protuberance immediately above the 

 isthmus and two rather larger ones across the centre. 

 Side view of semicell elongate-pyramidate, with a pro- 

 tuberance just above the base on each side, upper part 

 of margins concave, apex rounded. Vertical view 

 elliptic, poles broadly triangular with rounded angles ; 

 with two protuberances in the middle on each side, and 

 a third one between and beneath them ; polar lobe 

 broadly elliptic-oblong. Cell-wall punctate, punctula- 

 tions in vertical lines. 



