STAURASTRUM. 139 



plankton of Codale and Easedale Tarns ! Lancashire ! 

 W., N., and E. Yorks ! Cheshire (Roy). Cambridge ! 

 Warwicks ! Worcester ! Middlesex ! Surrey ! Sussex 



/ 



(Rolfs). Kent Hants ! (Roy}. Devon ! Cornwall ! 



WALES. General and abundant ! In the plankton ! 



SCOTLAND. General ! ; zygospores at Scotston Moor, 

 Aberdeen (Roy & Biss.). Near Lochmaddy, N. Uist, 

 Outer Hebrides ! Orkneys and Shetlands. and also in 

 the plankton ! 



IRELAND. Donegal ! Mayo and Clare Island ! 

 Galway ! Kerry, and in the plankton ! Dublin and 

 Wicklow (Arch.). Louth ! Armagh ! Lough Xeagh ! 

 Londonderry ! 



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

 ( Jalicia and Austria. Hungary. Italy. Norway. Sweden. 

 Bornhohn. N. Russia. Faeroes. Iceland. Nova Zembla. 

 Spitzbergen. Greenland. Siberia. Japan. Burma. 

 Siam (var.). Australia. New Zealand. Madagascar. 

 E. Africa. Azores. L T nited States and Alaska. Yukon. 

 Argentine. Patagonia. 



St. hexacerum is a very frequent species in this country, and 

 has a world-wide distribution. There have been different views 

 as to the range of St. hexacentm (Ehr.) Wittr. and St. tricorne Ralfs. 

 The latter includes two distinct forms, and of late years the earlier 

 name hexacerum has been almost universally adopted. Xordstedt 

 (in 'Bot. Notiser,' 1906, p. 115) has suggested that Ralfs' name 

 tricorne should be adopted for the form described by Ralfs as 

 St. tricorne var. /3, but this Desmid has been fully described and 

 figured by the late Prof. G. S. West as St. neglectum. 



Var. semicirculare Wittr. (PI. CXLII, fig. 15.) 



St. hexacerum var. semicirculare Wittr. Gotl. Ol. sotv. Alg. 1872, p. 52, 

 t. 4, f. 9 ; De Toni, Syll. Alg. 1889, p. 1206 ; West & G. 8. West, Alga-fl. 

 Yorks. 1902, p. 104 ; Freshw. Alg. Orkneys & Shetlands, 1905, p. 20. 



St. tricorne var. semicirculare West. Alg. W. Ireland, 1892, p. 180. 



St. hexacerum var. semilunare Roy & Biss. Scott. Desm. 1893, p. 21. 



Cells nearly twice as large as those of the typical 

 form ; semicells in front view subsemicircular ; in end 

 view triangular, with the sides slio'htlv concave, angles 



/o 



acutely rounded. 



