222 BRITISH DESMIDIACE^E. 



2. Spondylosium ellipticum W. & G. S. West. 



(PL CLXI, fig. 15.) 



Spondylosium elliplicum West & G. S. West, Alg. N. Ireland, 1902. p. 43, 

 t. 2, f. 21. 



Cells of medium size, about as long as broad, deeply 

 constricted, sinus open and acute ; semicells exactly 

 elliptical, apices convex, not flattened ; semicells in 

 side view subspherical ; from the end, elliptical ; 

 chloroplasts one in each semicell with a central pyrenoid. 

 Cells forming twisted colonies, with no mucous sheath. 



Zygospore unknown. 



Length 19 '6-24 ^ ; breadth 20-22 pi ; thickness 11*5- 

 12 pi ; breadth of isthmus 6 '7-7 \L. 



IRELAND.- -Lough Fea, Londonderry ! 



This species approaches S. ovale, Turn, (in 'Alg. E.Ind.' 1893, 

 p. 44, t. 18, f. 3, 9), but it is distinguished by its smaller size, 

 its relatively longer cells, its much deeper constriction, and by 

 the perfectly elliptical semicells. It is also more deeply con- 

 stricted in the side view than S. ovale, and only one pyrenoid is 

 present in a semicell. 



It also resembles to a certain extent S. planum (Wo lie) W. 

 .& G. S. West, but the more depressed semicells of the latter 

 species distinguish it. 



3. Spondylosium planum (Wolle) W. & G. S. West. 



(PL CLX, figs. 23-25.) 



Sphcerozosma pulchrum var. planum Wolle, Desm. U. S. 1884, p. 29, t. 4, 



f. 3, 4 ; De Toni, Syll. Alg. 1889, p. 794. 



Spondylosium ovale Turn. Alg. E. India, 1893, p. 44. t. 18, f. 3, 9. 

 Sp. pulchrum var. planum W. & G. S. West, Obs. Conj. 1898, p. 54 ; Scott. 



Freshw. Plankt. 1, 1903, p. 551. 

 Sp. planum W. & G. S. West, Periodic. Phytopl. Brit. Lakes, 1912, p. 430, 



t. 19, f. 5-8, 



Cells of medium size, about 1^ times broader than 

 long, subquadrangular, angles rounded, deeply con- 

 stricted, sinus obtuse, open ; semicells transversely 

 oblong, angles broadly rounded, apices flat ; in vertical 

 view oblong with rounded ends ; from the side sub- 



