MICRASTERIAS. 85 



Forma graimlata Racib. 



M. truncata forma grannlata Racib. Desm. Nowe, 1889, p. 105, t. 7, f. 1 ; 

 West, Alg. Eng. Lake Distr. 1892, p. 722 ; Alg. W. Ireland, 1892, p. 135. 



Cell-wall densely covered with irregular granules, 

 otherwise similar in form and size to the type. 

 ENGLAND.- -Hawkshead, Lancashire ! 

 IK ELAND. Ballynahinch and Lough Athry, Galway ! 

 Grog i'. Distribution. Austria. 



Var. Bahusiensis Wittr. (PI. XLII, fig. 9.) 



M. truncata var. Bahusiensis Wittr. Skandinav. Desm. 1869, p. 9, t. 1, f. 2; 

 West & G. S. West, Alg. S. England, 1897, p. 484. 



Cells with large outstanding polar lobes ; incisions 

 below the polar lobes widely open. 



Length 110 /LI; breadth 100 fi; breadth of polar lobe 

 83 /i. 



ENGLAND. Xew Forest, Hants ! 



SCOTLAND. Rhiconich, Sutherland ! 



Geogr. Distribution. Sweden. 



This variety is well-marked by reason of the outstanding 

 polar lobes. 



4. Micrasterias crenata Breb. 

 (PI. XLII, figs. 10-13.) 



Micrasterias crenata Breb. in Ealfs' Brit. Desm. 1848, p. 75, t. 7, f.2,t. 10, 

 f. 4; Arch, in Pritch. Infus. 1861, p. 727; Delp. Desm. subalp. 1873, 

 p. 92, t. 5,f. 17, 18; Cooke, Brit. Desm. 1886, p. 61, t. 28, f. 1; West, 

 Alg. N. Wales, 1890, p. 287; Alg. W. Ireland, 1892, p. 135; Roy & Biss. 

 Scott. Desm. 1893, p. 173 ; Nordst. Index Desm. 1896, p. 87 ; West & 

 G. S. West, Welw. Afric. Freshw. Alg. 1897, p. 87 ; Some Desm. U.S. 

 1898, p. 298 ; Alga-fl. Yorks. 1900, p. 66. 



Didymidium (Micrasterias) truncation forma a. crenatum Eeinscli, Algenfl. 

 Franken, 1867, p. 143. 



Micrasterias truncata forma c. Kabenh. Flor. Europ. Alg. Ill, 1868, p. 191. 



Cells small, about 14- times longer than broad, 



^ +) O 



elliptic with truncate poles, deeply constricted, sinus 

 narrowly linear; semicells 5-lobed, incisions between 

 the lobes linear, those below the polar lobe consider- 

 ably deeper than those between the lateral lobes ; polar 

 lobe very broadly cuneate, with a convex apex (some- 

 times a little flattened) and rounded angles ; lateral 



