COSMARIUM. 141 



Cell-wall much thinner than in the type, finely scro- 

 biculate and minutely punctate between the scrobicu- 

 1 at ions. 



Length 69-107 p; breadth 61-80 p.; breadth of 

 isthmus 28-33 /x ; thickness 40-44 /x. 



SCOTLAND.- -Plankton of Loch Shin, Sutherland ! 



Geogr. Distribution. T\ r . Africa. 



This variety was at first erroneously referred to C. Lundellii, 

 but the form of the semicells both in the front and vertical 

 view shows clearly that it is a thin- walled variety of C.pachy- 

 dermum. 



Careful examination of the cell-wall of this variety reveals 

 a large number of minute punctulatioiis scattered between the 

 larger ones. 



7. Cosmarium Ralfsii Breb. 

 (PL LVII, fig. 10 ; PI. LVIII, figs. 1, 2.) 



Cosmarium Ralfsii Breb. in Kalis' Brit. Desni. 1848,, p. 93, t. 15, f . 3 ; 

 Arch, in Pritcli. Infus. 1861, p. 731 ; Kabenh. Flor. Enrop. Alg. 1868, 

 III, p. 161 ; Lund. Desni. Suec. 1871, p. 52 ; Nordst. Xorges Desni. 

 1873, p. 25 ; Wolle, Desni. U.S. 1884, p. 69, t. 15, f. 1 ; Cooke, Brit. 

 Desni. 1886, p. 85, t. 36, f. 12 ; Hansg. Prodr. Algenfl. Bohm. 1888, 

 p. 193; West, Alg. N. Wales, 1890, p. 288; Alg. W. Ireland, 1892, 

 p. 163; Alg. Eng. Lake Distr. 1892, p. 729; Roy & Biss. Scott. Desm. 

 1894, p. 173 ; Nordst. Index Desm. 1896, p. 220 ; West & G-. S. West, 

 Alg. S. England, 1897, p. 485 ; Alga-fl. Torks. 1900, p. 68 ; Alg. K". 

 Ireland, 1902, p. 33. 



Didymidium (Cosmarium) Ralfsii Eeinscli, Algenfl. Frank. 1867, p. 108. 



Cosmarium Ralfsii a. typicum Klebs, Desm. Ostpreuss. 1879, p. 33, t. 3, 

 f. 33-35, 37 ;'Eacib. Norm. Desni. Polon. 1885, p. 70. 



Cosmaridium Ralfsii Hansg. Prodr. Algenfl. Bohm. 1888, p. 246. 



Pleurotseniopsis (Cosmaridium} Ralfsii (Breb.) De Toni, Syll. Alg. 1889, 

 p. 911. 



Cells large, subcircular, a little longer than broad, 

 very deeply constricted, sinus narrowly linear with a 

 dilated apex ; semicells subpyramidate-semicircular, 

 basal angles rounded, sides slightly convex, apex 

 broadly rounded or truncately rounded. Side view of 

 semicell subcircular. Vertical view rhomboid-elliptic, 

 ratio of axes about 1 : 1*9. Cell- wall finely punctate 

 or even scrobiculate, sometimes almost smooth. Chloro- 

 plasts parietal, consisting of several irregular bands 



