120 BRITISH DESMIDIACE^E. 



SCOTLAND. General! (Roy & Biss.). Not uncommon 



in the plankton ! Orkneys ! In the plankton, Shetlands ! 



IRELAND. Donegal ! Mavo and Clare Isle ! Galway ! 



o */ ^ 



Kerry ! Dublin and Wicklow (Arch.). 



Geogr. Distribution.- -France. Germany. Switzerland. 

 Galicia and Austria. Hungary. Italy. Turkey. Norway. 

 Sweden. Denmark. Bornholm. Central and S. Russia. 

 Faeroes. Iceland. Greenland. Siberia. Central China. 

 Japan. Ceylon. Burma, Australia. Madagascar. 

 Central Africa. Abyssinia. Azores. United States. 

 Guiana. Colombia. Brazil. Patagonia. 



Forma trigona Lund. (PL CXLIX, fig. 4.) 



St. tetracerum forma trigona Lund. Desm. Suec. 1871, p. 69 ; West, Alg. 

 W. Ireland, 1892, p. 187 ; West & G. S. West, Alg. S. England, 1897, 

 p. 495 ; Alg. Orkneys & Shetlands, 1905, p. 25. 



Cells in end view triradiate. 



Dimensions as in the biradiate form. 



ENGLAND. - -Lancashire ! Burnham Beeches, Bucks! 

 Surrey ! Hants ! Devon ! Cornwall ! 



WALES.- -Llyn Idwal and Moelfre, Carnarvonshire ! 



SCOTLAND.- -Bhiconich, Sutherland ! Bressay, Shet- 

 lands ! 



IRELAND. Mayo and Clare Isle ! Galway ! Kerry ! 



Geogr. Distribution. Sweden. 



Forma tetragon a W. & G. S. West. 



St. tetracerum forma tetragona West & G. S. West, Alg. S. England, 1897, 

 p. 495. 



Cells in end view 4-radiate. 

 ENGLAND.- -Koughton Moor, Cornwall ! 



Staurastrum tetracerum is a very characteristic and easily 

 recognised species with a world-wide distribution. The biradiate 

 form is the commonest ; the 3- and 4-radiate forms are com- 

 paratively rare. 



Bohlin ('Flor. Algol, d'eau douce d'Acores,' 1901, p. 56, f. 12) 

 has described and figured a rather large form of this species 

 under the name of St. gracillimum var. biradiatum. The same 

 author has also figured (fig. 13) a specimen intermediate in form 



