EUASTfilLM. 37 



This is a somewhat rare British species with very distinctive 

 characters, one of the most prominent being the large smooth 

 protuberance in the centre near the base of each semicell. 

 The large warts on either side of the apical incision, and near 

 the base of the polar lobe, are also very characteristic, but 

 were overlooked by Ralfs. In fact, the description of this 

 Desmid given by Ealfs is very incomplete, and has caused 

 many observers to go astray with regard to the exact identity 

 of E. rostratum. 



The Euastra figured by Wolle, 'Desm. U. S/ t. 27, figs. 8 

 and 9, as " E. rostratum " do not belong to this species. 



Note. E. rostratum var. cumbricum Benn. Freshw. Alg. 

 Eng. Lake Distr. II, 1888, p. 5, t. 1, f. 13. It is impossible 

 to say with certainty that Bennett's variety belongs to 

 E. roxtratum. His figure is too crude and the apex of the 

 semicell is most extraordinary. It would appear to differ 

 principally in the uniformity of the tabulation and the widely 

 excavated apex. Length 45-50 /LI ; breadth 25 /u. 



22. Euastrum Turnerii West. 

 (PL XXXVII, figs. 9, 10.) 



"Euastrum sp. ad. E. denticulatum accedens " Xordst. Freshw. Alg. N. 



Zeal. 1888, p. 35, t. 3, f. 11 [. denticulatum Mask., 1889, uon Gay]. 

 Euastrv.m Turnerii West Alg. W. Ireland, 1892, p. 141, t. 20, f. 18 



Nordst. Index Desui. 1896, p. 264 ; West & G. S. West, Alg. N. Ireland 



1902, p. 29. 



Cells small, about 1^ times longer than broad, deeply 

 constricted, sinus narrowly linear with a dilated ex- 

 tremity; semicells pyramidate, more or less three- 

 lolled ; polar lobe short and very broad, oblong-rect- 

 angular, lateral margins retuse, apical angles furnished 

 with a short divergent spine, apex truncate, with four 

 undulations and a narrow median incision ; lateral 

 lobes bilobulate, both upper and lower lobules truncato- 

 emarginate ; semicells with a small tumour in the 

 centre ornamented with a rine; of granules. Cell-wall 



o o 



furnished with a number of granules within the polar 

 and lateral lobes. Side view of semicell ovate pyrami- 

 date, apex acute, with a truncate granulate protuber- 

 ance near the base on each side. Vertical view elliptic, 



