142 BRITISH DESMIDIACE^C. 



Geogr. Distribution. Lappmark in Xorway (forma). 



Schmidle (' Lappmark Siisswasseralgen/ 1898, p. 59, t. 3, 

 f . 9) lias described a " forma lapponica ' of this variety in 

 which the cells are smaller and narrower, with subtruncate 

 apices and slightly thickened angles ; length 52 JJL, breadth 

 45 ju. 



11. Staurastrum tumidum Breb. 

 (PL CXXIL figs. 1-5.) 



Binatella tumida Breb. Alg. Falaise, 1835, p. 269. 



Staurastrum tumidum Breb. in Ralfs' Brit. Desin. 1848, p. 126, t. 21, f. 6 ; 

 Arch, in Pi-itch. Infus. 1861, p. 741 ; Eabenli. Flor. Europ. Alg-. III, 

 1868, p. 201 ; Lund. Desm. Suec. 1871, p. 72, t. 4. f. 10; Wolle/Desm. 

 U. S. 1884, p. 120, t. 39, f. 1, 2 [figures poor] ; Cooke, Brit, Desm. 1887, 

 p. 165, t. 55, f. 8, t. 57, f. 1 ; De Toni, Syll. Alg. 1889, p. 1201 ; West, 

 Alg. W. Ireland, 1892, p. 180 ; Alg. Engl. Lake Distr. 1892, p. 732 ; 

 Roy & Biss. Scott. Desm. 1893, p. 244 (sep. p. 26) ; Nordst. Index Desm. 

 1896, p. 263 ; W. & GK S. West, Alg. S. England, 1897, p. 494; Schmidle, 

 Lappmark Siisswasseralgen, 1898, p. 58 ; W. & G. S. West, Alga-fl. 

 Yorks. 1901, p. 103 ; Further Contrib. Freshw. Plankton Scott. Lochs, 

 1905, p. 486 ; Brit. Freshw. Phytoplaiikton, etc., 1909, p. 183. 



Phycastrum tumidum Klitz. Spec. Alg. 1849, p. 179. 



Pleitrenterium tumidum (Breb.) Wille in Engler & Prantl, Natiiii. Pflan- 

 zeiifam. 1890, p. 11. 



Tempered tumida (Breb.) Bougon in Le Micrographe preparateur, v, 1897, 

 p. 68. 



Cells very large, a little longer than broad, deeply 

 constricted, sinus open and acute-angled with a slightly 

 rounded apex ; semicells very broadly subelliptic, apex 

 generally a little flattened and sometimes faintly con- 

 cave in the middle, lateral angles with a small button- 

 like thickening, which is sometimes replaced by a 

 small, solid mamilla. Vertical view triangular (rarely 

 quadrangular), with strongly convex sides, and a small 

 projecting mamilla at each angle. Cell- wall punctate. 

 Chloroplasts forming 4-6 (?) parietal cushions in each 

 semicell. 



Zygospore ovoid-oblong, with a thick lamellose 

 wall, furnished with a few, irregularly scattered, 

 conical papillae. 



Length 112-134 p; breadth 90-127 /*; breadth of 

 isthmus 44-50 p, ; length of zygosp. without papillae 

 176 jit, breadth 92 p,; length of papillae 14 /.t. 



ENGLAND. Cumberland! Westmoreland! (Bissett). 



