MICRASTEEIAS. 95 



Length 163 /x; breadth 151 /x; breadth of isthmus, 

 16 fji. 



SCOTLAND. In the plankton of Loch Doon, Ayr- 

 shire ! 



This variety is of great interest as only one other triangular 

 form of Micrasterias is known to occur, viz. M. pinnatifida 

 (Kiitz.) Ralfs var. trigona West (' Freshw. Alg. Maine/ 1889, 

 p. 206; in ' Journ. Bot./ 1889, t. 291, f. 15). 



9. Micrasterias Sol (Ehrenb.) Kiitz. 

 (PL XLVI, figs. 1, 2.) 



Euastrum Sol Ehrenb., Verbreit. imd Einfhiss mikroskop. Lebens in Siid- 



iind Nord-amerika, Physik. Abh. Preuss. Ak. Wiss. zu Berlin, 1841 



(Berlin, 1843), p. 413, t. 4, f. 16. 

 Hicrasterias radiosa Ealfs, Brit. Desm. 1848, p. 72, t. 8, f. 3; Arch, in 



Pritch. Infus. 1861, p. 727, t. 1, f. 21 ; Eabenh. Flor. Europ. Alg. Ill, 



1868, p. 192; Delp. Desm. subalp. 1873, p. 85, t. 4, f. 2-4; Wolle, Desm. 



U.S. 1884, p. 109, t. 31, f. 2, 3 ("figures badl ; Cooke, Brit. Desm. 1886, 



p. 59, t. 27, f. 1; De Toni, Syll. Alg. 1889, p. 1133; West, Alg. W. 



Ireland, 1892, p. 134; Eoy & Biss. Scott. Desm. 1893, p. 174; Nordst. 



Index Desm. 1896, p. 219 ; West & G-. S. West, Alg. S. England, 1897, 



p. 484 ; Scott. Freshw. Plankton, I, 1903, p. 525. 

 M. Sol (Ehrenb.) Kiitz. Spec. Alg. 1849, p. 171; Jacobs. Desm. Danem. 



1875, p. 188. 

 Helierella Sol (Ehrenb.) Kuntze Eev. gen. plant, 1891, p. 897. 



Cells approximately circular in outline, very deeply 

 constricted, sinus slightly open with each margin 

 faintly 2- or 3-undulate ; semicells deeply 5-lobed, 

 with the incisions between both the lobes and lobules 

 deep and slightly open, sometimes open inwards but 

 closed outwards ; polar lobe with subparallel sides, 

 slightly expanded at the apex, apical margin retuse- 

 emarginate, each angle emarginate-dentate, with a 

 small tooth attached within the apical margin near the 

 angle on each side ; lateral lobes unequal, superior 

 lateral lobes slightly larger than inferior lateral lobes 

 and generally (but not always) more subdivided; in- 

 ferior lateral lobes divided into four equal lobules by 

 three incisions, the median one being much deeper 

 than the other two, each lobule furcate-dentate at the 

 extremity (or sometimes further divided into two fur- 



t/ \ 



cate-dentate portions of equal size) ; superior lateral 



