202 BRITISH DESMIDIACE/E. 



C. pusillum Hilse is one of the smallest species of the genus r 

 and is very rare. It is uncertain whether the delicate connecting 

 strands between the cells are single or double. C. pusillum is 

 distinguished from C. perissum and C. pulchellum by the special 

 characters of its colonies, and by its cells equal in length to their 

 breadth, with oblong semicells and deep, linear sinus. 



That C. subramosum Schmidle is synonymous with C. pusillum 

 Hilse was pointed out by Dr. Liitkemuller in a letter to the late 

 Professor G. S. West in 1912. Dr. Liitkemuller had carefully 

 examined the original specimens of Hilse in Kabenhorst's 'Alg. 

 Exs.' no. 1963, and compared them with preserved material of 

 C. subramosum identified by Schmidle. He came to the con- 

 clusion that the two were identical both in the form of their cells 

 and the character of the colonies. 



5. Cosmocladium Saxonicum De Bary. 

 (PL CLVIII, figs. 13-16.) 



Cosmocladium Saxonicum De Barv, Cosmocladium, 1865, pp. 321-9, t. 4, 

 f. 1-3 ; Arch, in Quart. Journ. Micr. Sci. vol. 7, 1867, p. 298 ; Pxabenh. 

 Flor. Eur. Alg. 1868, p. 54 ; Arch, in Quart, Journ. Micr. Sci. 1874, p. 212 ; 

 Cooke, Brit. Desm. 1887, p. 78, t. 35, f. 16; De Toni, Syll. Alg. 1889, 

 p. 804 ; Roy & Biss. Scott. Desm. 1893, p. 63 ; ? West & G. S. West, Alg. 

 S. England,' 1897, p. 492 ; Schroder, Cosm. Saxomcum, 1900, p. 15. t. 1 ;. 

 Ltitkem. Zellm. Desm. 1902, p. 359, t. 18, f. 34-36 : West & G. S. West, 

 Notes Alg. III. 1903, p. 10 ; Comp. Study Plankt. Irish Lakes, 1906, 

 p. 102 ; Kofoid, Plankt. 111. River, 1908, p. 61 ; West & G. S. West,. 

 Brit, Freshw. Phytoplankton, 1909, p. 168. 



Cells larger than in any other British species of the 

 genus, about li times longer than broad, deeply con- 

 stricted, sinus acute angled, opening widely; semicells 

 subelliptic-reniform, dorsal margin much more convex: 

 than the ventral ; in vertical view elliptic ; chloroplasts 

 axile, with one pyrenoid in each semicell, and 4 lobes 

 projecting from the central mass towards the cell- wall. 

 Cells united by 2 parallel gelatinous filaments into 

 colonies of varying size, consisting only of 2 or 3 cells, 

 or up to 90 in a single colony ; colonies free-floating, and 

 sometimes immersed in a delicate jelly ; cells usually 

 parallel to each other, and with their broad faces 

 perpendicular to the direction of the strings, so that 

 normally their side view is presented to the observer. 



