102 BRITISH DESMIDIACE.E. 



Length 21-25 /^ ; breadth 17-19ju; breadth of 

 isthmus 6*5-7*5 p.. 



E NGLAND.- -Cumberland ! Westmoreland! W., JST., 

 and E. Yorks ! Cambs ! Oxfordshire ! Middlesex ! 

 Surrey ! Kent ! Cornwall ! 



WALES. Llvn-an-afon, Carnarvonshire ! 



& 



SCOTLAND. - Bhiconich, Sutherland ! Inverness ! 

 Perth ! Orkneys ! Shetlands ! 



IK ELAND.- -Not uncommon! Plankton of Lough 

 Corrib, Gal way ! 



Geogr. Distribution.- -Germany. Sweden. Portugal. 

 Bosnia. Nova Zembla. Greenland. Azores. United 

 States. 



This variety has usually been regarded as one of the forms 

 of C. Meneghinii, but we think it has greater affinities with 

 C. l&ve than with C. Meneghinii. It has a wide distribution 

 in the British Islands, but does not appear ever to be 

 abundant. 



Var. septentrionale Wille. (PI. LXXIII, figs. 22-25.) 



C. Iseve Eabenli. var. septentrionale Wille, Ferskv. Alg. Nov. Senilj. 1879, 

 p. 43, t. 12, f. 34; West, Desm. Massachusetts, 18S9, p. 18, t. 3, f. 19 ; 

 De Toni, Syll. Alg. 1889, p. 935 ; West & G. S. West, Alg. S. England, 

 1897, p. 487 ; G. S. West, Alga-fl. Cambr. 1899, p. 216; Variation Desin. 

 1899, p. 387, t. 10, f. 7-9; West & G. S. West, Alga-fl. Yorks. 1900, 

 p. 94 ; Freshw. Alg. Ceylon, 1902, p. 166 ; Alg. N. Ireland, 1902, p. 35 ; 

 Scott. Freshw. Plankton, I. 1903, p. 527 ; Freshw. Alg. Orkneys and 

 Shetlands, 1905, p. 23. 



Cells bexagonal ; semicells with rectangular basal 

 angles, lower third of the sides parallel or slightly 

 outwardly divergent, upper two-thirds (superior lateral 

 margins) convergent, straight, slightly retuse, or 

 biundulate, apex narrowly truncate and retuse (some- 

 times almost emarginate) ; vertical view with sub- 

 truncate poles ; side view of semicell broadly or 

 narrowly ovate- elliptic. Cell-w T all smooth. 



Length 24-28 p.; breadth 15-22 /x ; breadth of 

 isthmus 4'8-6'5/x; thickness 9-1 3 p.. 



ENGLAND.- -Westmoreland ! Lancashire ! W. and 

 N. Yorks ! Leicestershire (-Roy). Essex ! Cambs ! 

 Middlesex ! Surrey ! 



