86 BRITISH DESMIDIACEvE. 



lobes bilobulate (rarely entire), lobules rounded-trun- 

 cate or very slightly retuse. Side view of semicell 

 widely ovate. Vertical view fusiform-elliptic. Cell- 

 wall smooth. 



Zygospore unknown. 



Length 75-125^; breadth 54-102 /u; breadth of 

 polar lobe 46-65 /*; breadth of isthmus 17-30^. 



ENGLAND. Westmoreland (Bissetf). W. and N. 

 Yorks ! Warwick (Wills). Sussex (Ral/s). Cornwall 

 (Marquand). 



WALES. Near Dolbadarn Castle ! , Bethesda ! , 

 Capel Curig (Gooke Wills), and Snowdon (Roy), 

 Carnarvonshire. Dolgelly, Merioneth (Ralfs). 



SCOTLAND. Ross, Inverness, Aberdeen, Kincardine, 

 Forfar, Perth !, Argyll, Arran, Fife (Roy $ Bissett). 



IRELAND. Kylemore, and Loughs between Clifden 

 and Round stone, Glalway ! 



Geogr. Distribution. France. Germany. Austria 

 and Gralicia. Poland. Italy. Norway. W. Africa. 

 United States. Brazil. 



The typical form of M. crenata seems very distinct from 

 M. truncata. It is proportionately longer, with a more robust 

 and deeper polar lobe, which is never retuse in the middle, 

 though often flattened. The lateral angles of the polar lobe 

 are rounded, and the lateral lobes are not so deeply incised as 

 in M. truncata, the lobules possessing at the same time 

 rounded angles. 



It is unquestionably a rare species, although many forms 

 have been recorded intermediate in character between it and 

 truncata. 



5. Micrasterias Jenneri Ralfs. 

 (PI. XLII, fig. 14; PI. XLIII, figs. 1, 2.) 



Micrasterias Jenneri Ralfs, Brit. Desin. 1848, p. 76 (a and f3), t. 11, f. 1 ; 



Arch, in Pritch. Infus. 1861, p. 727 ; Rabenh. Flor. Europ. Alg. Ill, 



1868, p. 194 ; Cooke, Brit, Desm. 1886, p. 62, t. 28, f . 3 ; Hansg. Prodr. 



Algenn. Bohm. 1888, p. 209 ; De Toni, Syll. Alg. 1889, p. 1125 ; West, 



Alg. N. Wales, 1890, p. 287 ; Alg. W. Ireland, 1892, p. 135 ; Alg. Eng. 



Lake Distr. 1892, p. 722; Roy & Biss. Scott. Desm. 1893, p. 174; 



Kordst. Index Desm. 1896, p. 150 ; West & G. S. West, Alg. S. England, 



1897, p. 484. 

 Helierella Jenneri Kuntze, Revis. gen. plant. 1891, p. 898. 



