130 BRITISH DESM1DIACE;E. 



basal angles rectangular, margin at the base crenate- 

 denticulate (which appearance is due to a basal ring 

 of longitudinally compressed denticulate verruca?), 

 apex truncate-convex, furnished with about 7 emargi- 

 nate verrucas at the margin and about 6 denticulate 

 verrucas within the dorsal margin. Vertical view 

 triangular-subcircular or quadrangular-subcircular, 

 entire margin furnished with emarginate verrucas, 

 and with a series of verrucas within the margin. 



o 



Zygospore unknown. 



Length 47'5 p. ; breadth of base of semicells 31*5 //,, 

 of apex 31 '5-3 3' 3 //, ; breadth of isthmus 25 p,. 



Nordstedt mentions the two following forms : 



Forma trigona.- -Vertical view triangular-circular, 

 with 15 (= 3 x 5) marginal verrucas, with 9 

 (= 3 X 3) within the margin, and usually with 18 

 (=3 x 6), more rarely with 16 or 17, basal verrucas. 



Forma, tetragona. Vertical view quadrangular-cir- 

 cular, with 20 (= 4 X 5) marginal verrucas, with 12 

 (=4 x 3) within the margin, and usually with 20 

 (=4 X 5), more rarely with 19, basal verrucas. 



SCOTLAND.- -On the table-land north-west of Can- 

 lochan, Aberdeen (or Forfar ?) (Roy fy Bissett). 



Geogr. Distribution.- -Spitzber gen. Nova Zembla. 



We have not yet seen this characteristic arctic Desmid. It 

 is so distinctive that it scarcely needs comparison with any 

 other species of the genus. 



SECTION B. 

 Cells subcylindrical, smooth. 



5. Staurastrum minutissimum Reinsch. 

 (PI. CXIX, fig. 2.) 



Staurastrum minutissimum Keinsch, Spec. Gen. Alg. 1867, p. 140, t. 23 

 A II, f. 3-8 ; ? Kabenh. Flor. Europ. Alg. Ill, 1868, p. 201 ; Eeinsch, 

 Contrib. Alg. et Fungi, 1875, p. 91, t. 16, f. 3 [forma] ; De Toni, Syll. 

 Alg. 1889, p. 1184 ; Borge, Siisswasseralgen Franz Josefs-Land, 1899, 

 p. 763. 



Didymidium (Staurastrum] minutissimum Eeinsch, Algenfl. Frank. 1867, 

 p. 153, t. 13, f. 1. 



