EUASTRUM. 39 



Vertical view elliptic, with pointed and denticulate 

 poles, lateral margins granulate or denticulate, and 

 with a broad emarginate protuberance at the middle 

 on each side. 



Zygospore globose, furnished with numerous, rather 

 bluntly-pointed spines. 



Length 28-38'5/x; breadth 18-23 p.; breadth of 

 isthmus 5'5-6*5ft; thickness 12'5-13*5 p. ; diam. 

 zygosp. without spines 26-30 /x ; length of spines 

 7'5-9'6 p.. 



ENGLAND. Cornwall (Ra Ifo) . 

 Dolgelly (Ralfs). 



IRELAND. Dublin and Wicklow (Archer). 

 Geogr. Distribution. Germany. Sweden. India. 

 United States. Guiana. 



We think E. spinosum Ralfs possesses sufficiently distinctive 

 characters to allow of its remaining as a distinct species. The 

 gently-sinuate margins of the semicells, the absence of any 

 trace of a " neck/ 7 and the spines on the lateral margins, dis- 

 tinguish it from ordinary forms of E. elegans. Ralfs also 

 states that the zygospore possesses more slender and more 

 numerous spines than that of E. elegans. 



The Euastra figured by Wolle, ' Desm. U. S.' t. 27, figs. 4-7, 

 as {t E. spinosum" do not belong to this species. 



24. Euastrum bidentatum Nag. 

 (PI. XXXVII, figs. 16-19.) 



Euastrum bidentatum Nag. Gatt. einzell. Alg. 1849, p. 122, t. 7 D, f. 1 a-f; 



West & G. S. West, Alsra-fl. Yorks. 1900, p. 62 ; Alg. N. Ireland, 1902, 



p. 29. 

 E. elegans (Breb.) Kiitz. var. bidentatum (Nag.) Jacobs. Desm. Danern. 



1875, p. 191 ; Borg. Bornhohn. Desm.-fl. 1889, p. 143, t. 6, f . 2 ; Borge, 



Chlorophy. Norska Fimnark. 1892, p. 6 ; Eoy & Biss. Scott. Desin. 1893, 



p. 176 ; Borg. Ferskv. alg. Ostgronl. 1894, p. 31 ; West & G. S. West, 



Alg. S. England, 1897, p. 483. 

 E. elegans (Breb.) Kiitz. var. speciosum Boldt, Desmid. Gronland, 1888, 



p. 9, t. 1, f. 10, 11 ; De Toni, Syll. Alg. 1889, p. 1102 ; Schmidle, Beitr. 



alp. Alg. 1895, p. 22. 



Cells small, about li- times longer than broad, deeply 

 constricted, sinus narrowly linear with a dilated ex- 

 tremity; semicells subpyramidate, with bilobulate 



