CCKSMAKIUM. 205 



186. Cosmarium Arnellii Boldt. 

 (PI. LXXXIY, fig. 11.) 



Cosmarhun Arnellii Boldt, Siber. Chlorophy. 1885, p. 107, t. 5, t. 15; De 



Toni, Syll. Alg. 1889, p. 994 ; Xorclst. Index Desm. 1896, p. 52. 

 U'rsinella Arnellii Knntze, E-evis. gen. plant. 1891, p. 924. 



Cells rather under medium size, about 1J times as 

 long as broad, deeply constricted, sinus narrowly 

 linear ; semicells trapeziform-semicircular, basal angles 

 rectangular and very slightly obtuse, lower parts of 

 sides perpendicular, upper parts rapidly converging 

 towards the widely truncate apex ; cell-wall finely 

 granulate, granules in oblique series or more or less 

 irregular, with three transverse series of larger 

 granules across the central part of the semicells. Side 

 view of semicell circular. Vertical view elliptic with 

 slightly pointed poles, granules in transverse series. 



Zygospore unknown. 



Length 62 p. ; breadth 50 JJL ; breadth of isthmus 

 21 fj. ; thickness 24 JJL. 



Geogr. Distribution.- - G-alicia in Austria (var.). 

 Siberia. 



C. Arnellii is somewhat related to C. punctulatum, but 

 differs in its much larger size, in the shape of its semicells,, 

 in the three prominent series of granules across the centre of 

 the semicells, and in the more attenuated poles of the vertical 

 view. The typical form is not known to occur in the British 

 Islands. 



Forma compressa AVest. (PL LXXXIV, fig. 12.) 



C. Arnellii Boldt forma compressa West, Alg. W. Ireland, 1892, p. 154, 

 t. 21, f. 10. 



Cells rather smaller and relatively wider than the 

 type, with the three transverse series of granules in 

 the central region of the semicells somewhat more 



o 



distinct and nearer the isthmus. 



Length 42 //, ; breadth 37 /x ; breadth of isthmus 16 p.. 



IRELAND. Small lakes between Clifden and Round- 

 stone, Galway ! 



