CLOSTERIUM. 127 



Tho typical form of this variety has not been observed 

 from the British Islands, but Turner has described a form 

 of it. 



Var. sculptum Racib. forma eboracensis Turner. 



Closterium intermedium var. sculptum Eacib. forma eboracensis Turner, 

 Desm. Notes, 1893, p. 31(5, f. 17 ; West & G. S. West, Alga-fl. Yorks. 

 190O, p. 55. 



This form differs from Raciborski's in the possession 

 of dilated apices. 



Length 410 /JL; breadth 21 '5 /A; breadth of apices 15/x. 



ENGLAND. Strensall Common, N. Yorks (IT. B. 

 Turner). 



12. Closterium Ulna Focke. 

 (PI. XIV, figs. 7-0.) 



Closterium Ulna Focke, Phys. Stud. 1847, p. 59, t. 3, f. 30; Nordst. Index 

 Desm. 1896, p. 265 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 55 ; 

 Alg. N. Ireland, 1902, p. 24. 



Closterium directum Arch. Descript. new Cosm., etc., 1862, p. 249, t. 12, 

 f. 23 and 24; Kabenh. Flor. Europ. Algar. Ill, 1868, p. 127; Cooke, 

 Brit. Desm. 1886, p. 18, t. 8, f. 3 ; Nordst. Freshw. Alg. N. Zeal. 1888, 

 p. 69 ; West, Alg. W. Ireland, 1892, p. 120 ; Eoy & Biss. Scott. Desm. 

 1894, p. 244 ; Borge, Siissw. Chlor. Archang. 1894, p. 14 ; Nordst. Ind.-x 

 Desm. 1896, p. 110 ; West & G. S. West, Alg. S. England, 1897, p. 482. 



Cl. striolatum var. Ulna Jacobs. Desm. Danem. 1875, p. 175. 



Cl. intermedium b. directum Klebs, Desm. Ostpreuss. 1879, p. 16, t. 2, f. 17. 



ArthrmUa directa Knntze, Eevis. gen. plant. 1891, p. 883. 



Cells of medium size, 16-20 times longer than their 

 diameter, very slightly curved, outer margin from 15 

 to 2o of arc, inner margin not tumid, almost parallel 

 to the outer margin, very slightly attenuated to the 

 apices, which are truncate ; cell-wall colourless or pale 

 yellow, very finely striated, with 1420 striae visible 

 across the cell ; each chloroplast with 5 or 6 indistinct 

 ridges and a median series of 6 or 7 pyrenoids ; 

 terminal vacuoles generally with one large moving 



granule. 



o 



Zygospore unknown. 

 Length 220-480^; breadth 11-22 /x ; breadth of 

 apices 8'5-12 p. 



