STAURASTRUM. 179 



^ Geogr. Distribution.- -Finland. India, Central Africa. 

 United States. 



This species exhibits a certain amount of variation in size, 

 in the form of the body, and in the length of the processes. 

 There are two whorls of processes on each semicell, the lower 

 whorl consisting (in the triradiate form) either of 3 processes 

 (one at each angle), or of 9 processes (one at each angle and a 

 pair on each lateral margin), and the upper whorl consisting of 

 6 processes. Thus the total number of processes on each semi- 

 cell is either 9 or 15 in the triradiate form. Each process is 

 very slightly dilated at the end, and is usually bifurcate, occasion- 

 ally trifurcate, and the lobes are hollow to the tip. 



Var. trifurcatum W. & G. S. West. (PI. CLV, figs. 



13, 14.) 



St. TohopeJcaligense var. trifurcatum West & G. S. West, Alg. Madagas. 1895, 

 p. 80, t. 9, f. 8 ; Alg. Ceylon, 1902, p. 181, t. 21, f. 27 ; Further Contrib. 

 Plankton Scott. Lochs, 1905, p. 503, t. 7, f. 7. 



This variety is characterised by its slightly shorter 

 processes, with strong trifid spreading apices ; processes 

 usually 3 at each angle, less spreading in the front view. 

 Chloroplast axile with a central pyrenoid. 



Length, without processes, 36-45 (x ; including pro- 

 cesses, 54-75 (Ji ; breadth, without processes, 27-32 y* ; 

 including processes, 50-70 pt ; breadth of isthmus 9'5- 



14(JL. 



SCOTLAND.- -Rhiconich, Sutherland ! Plankton of 

 Loch Fadaghoda, Lewis, Outer Hebrides ! 



Geogr. Distribution. Ceylon. Australia. Madagascar. 



This variety, like the type, exhibits considerable variation. 

 The British examples had always the smaller number of pro- 

 cesses in the lower whorl, i. e. 3 in the triangular form and 4 in 

 the quadrangular form, but specimens from Ceylon have been 

 seen in which there were 9 lower processes in a triangular speci- 

 men. The trifid apices of the processes are not constant either, 

 for in the specimens from Loch Fadaghoda the processes of the 

 upper whorl were frequently bifid. 



