STAUEASTEUM. 171 



158. Staurastrum dorsidentiferum W. & G. S. West. 



(PL CXLVIII, fig. 4.) 



Staurastrum dorsidentiferum West & G. S. West, Coinp. Study Plankton 

 Irish Lakes, 1906, p. 103, t. 11, f. 10; British Freshw. Phytoplankton, 

 1909, p. 202. 



Cells large, about 1^ times broader than long, including 



O ' * O O 



the processes, constriction fairly deep, sinus open and 

 obtuse at the apex ; semicells smooth and cup-shaped, 

 apex generally flattened and gently undulate, angles 

 produced to form long stout processes projecting nearly 

 horizontally, and tipped with 4 teeth ; lower margin of 

 each process crenulate, upper margin also ere mil ate, but 

 the median 3-6 (usually 5) crenations bearing acute, 

 erect teeth ; vertical view triangular, sides slightly 

 convex, angles produced to form long processes, with 

 undulate margins, and a single row of spines along each. 



Zygospore unknown. 



Greatest length 75-79 \ ; breadth, without processes, 

 about 48 {Jt ; with processes, 1 08-1 20 [i ; breadth of 

 isthmus 1 8 [A. 



IRELAND. --Plankton of Loughs Conn and Cullin, 

 Mayo ! Lough Corrib, Gal way ! 



The direction of the processes in the front view is somewhat 

 variable. In some specimens they are rather upwardly diver- 

 gent, but in the majority they are horizontally disposed. The 

 number of teeth affixed to the crenations of the upper margins of 

 the processes is also variable, even on the processes of the same 

 plant. The species is confined to plankton and should be 

 compared with St. gracile Ralfs and St. Sebaldi Reinsch. Its 

 large cells, smooth except for the row of stout spines on the top 

 of each process, distinguish it from all other species. 



159. Staurastrum aciculiferum (West) Anders. 

 (PL CXXXIV, fig. 6.) 



St. Aricitla Tar. aciculiferum West, Add. Alg. W. Yorks. 1889, p. 293, 



t. 291, f. 12 ; Alg. N. Wales, 1890, p. 16. 

 St. aciculiferum Anders. Sverig. Chlor. 1890, p. 11, t. 1, f. 4; West & G. S. 



West, Alga-fl. Yorks. 1902, p. 98 ; Alg. N. Ireland, 1902, p. 47 ; Borge, 



Beitrage Alg. Schweden, 1906, p. 45. 



