140 BRITISH DESMIDIACE&. 



wliicli it differs in its oblong semicells and in the elongation 



o o 



of the isthmus. 



The Desmid figured by Bohliii from the Azores under the 

 name of " St. coarctatum var. subcurtum' (Cf. Bolilin, 'Flor. 

 Algol, d'eau douce d. A9ores/ 1901, t. 1, f. 27) is probably a 

 small form of St. elllpticiun. 



10. Staurastrum grande Bulnh. 

 (PL CXIX, figs. 11-13; PI. CXX, fig. 1.) 



Staurastrum grande Bulnh. in Hedwigia, 1861, p. 51, t. 9, f . 14; Lund. 

 Desni. Suec. p. 72 ; Cooke in Grevillea, ix, 1881, p. 91, t. 139, f. 4 ; 

 Wolle, Desm. U. S. 1884, p. 120, t. 39, f. 3, 4 ; Cooke, Brit. Desni. 1887, 

 p. 166, t. 57, f. 2 ; De Toiii, Syll. Alg. 1889, p. 1201 ; Borg. Desm. 

 Brasil. 1890, p. 51 ; West, Alg. Engl. Lake Distr. 1892, p. 732 ; Koy & 

 Biss. Scott. Desm. 1893, p. 238 ; Johnson, Rare Desm. U. S. II, 1895, 

 p. 294; Nordst. Index Desm. 1896, p. 134; W. & G. S. West, Scott. 

 Freshw. Plankton, I. 1903, p. 547 ; Further Contrib. Freshw. Plankton 

 Scott. Lochs, 1905, p. 486 ; Cushmaii in Bull. Torr. Bot. Club, xxxii, 

 1905, p. 227, t. 8, f . 17 ; in Khodora, vii, 1905, p. 262 ; W. & G. S. West, 

 Comp. Study Plankton Irish Lakes, 1906, p. 86 ; G. S. West, Alt;-. Yan 

 Yean, 1909, pp. 15, 27 ; W. & G. S. West, Brit. Freshw. Phytoplankton, 

 etc., 1909, p. 182 ; Phytoplankton Engl. Lake Distr. 1909, p. 139. 



St. grande forma Lund. Desm. Suec. 1871, p. 72, t. 4, f. 11 ; Liitkem. 

 Desm. Bohm. 1910, p. 498. 



Pleurenterium grande (Bulnh.) Wille in Engler & Prantl, Naturl. 

 Pflanzenfam. 1890, pp. 11, 12 (f. 7 G). 



Cells large, about as long as broad, deeply constricted, 

 sinus acute-angled; semicells elliptic or subeliiptic, 

 sometimes with the ventral margin more convex than 

 the dorsal margin, lateral angles rather acutely rounded. 

 Vertical view triangular, or very rarely quadrangular, 

 sides slightly retuse, angles acutely rounded. Cell- 

 wall finely punctate. Chloroplasts axile, or sometimes 

 parietal, 3-6 in each semicell, each with 13 pyre- 

 noids. 



Zygospore angular-globose, furnished with scattered 

 stout spines, arising from a dilated base and often 

 curved. 



Length 84-100 /x; breadth 80-11 1/x,; breadth of 

 isthmus 21-25 jut; diam. zygosp. (of rather small form) 

 without spines 60 ^, with spines 100 JJL. 



ENGLAND.- -Borrowdale, Cumberland ! Lough rigg, 

 and near Bowness ; also plankton of Brothers' Water, 

 Westmoreland ! 



