STAURASTRUM. 141 



140. Staurastrum Cerastes Lund. 

 (PL CL, fig. 16; PL CLI, fig. 1.) 



Cerastes Lund. Desrn. Suec. 1871. p. 69, t. 4, f. 6; Wills in 

 Midland Naturalist, 1881, p. 16, t. 5, f. 8 ; Wolle, Desm. U. S. 1884, p. 133, 

 t, 43, f. 6, 7 ; Cooke, Brit. Desm. 1887, p. 173, t. 59, f. 3 ; De Toni, Syll. 

 Alg. 1889, p. 1213 ; Roy & Biss. Scott. Desm. 1893, p. 18 ; West & G. S. 

 West, Some N. Amer. Desm. 1896, p. 268, t. 18, f. 4 ; Desm. U. S. 1898, 

 p. 318 ; Brit. Freshw. Phytoplankton, 1909, p. 174. 

 Staurastrum sp. Archer in Quart. Journ. Micr. Sc. vol. 12, 1872, p. 202. 



Cells of medium size, about as long as broad, or some- 

 times broader, constriction small, an acute notch ; semi- 

 cells almost cylindrical in the lower part, widening 

 considerably upwards ; apex strongly convex, lateral 

 angles produced to form stout processes, attenuated 

 towards their apices, and gracefully incurved so that 

 the processes of the two semicells are nearly in contact ; 

 upper margin of process verrucose (in some aspects the 

 apex of the semicell also is verrucose), about 9 verrucae 

 visible along each process, becoming more crowded and 

 simpler towards the apex of the process ; lower margin 

 smooth ; with another series of verrucae stretching hori- 

 zontally from tip to tip of adjacent processes across the 

 face of the semicell, and a further series of granules round 

 its base. Vertical view 3- or 4-angled, angles produced 

 into short tapering processes, lateral margins concave and 

 verrucose, and with another curved series of verrucse 

 stretching from angle to angle just within each margin. 

 Chloroplast axile, with a central pyrenoid in each semi- 

 cell. 



Zygospore unknown. 



Length 48-57 \L ; breadth, including processes, 58- 

 72 \L ; breadth of isthmus 10-12[ji. 



WALES. Capel Curig, Carnarvonshire ! (Cooke & 

 Wills). In the plankton ! 



SCOTLAND. Near Loch Dawan, Aberdeen (Roy & 

 Biss.). Rhiconich, Sutherland! 



IRELAND. Galway (Arch.) . 



Geogr. Distribution. Norway. Sweden. Finland. 

 Ceylon (var.). United States. 



This is one of the most beautiful of Desmids. Its granulation 



