204 BRITISH DESMIDIACE.E. 



185. Cosmarium quaternarium Xordst. 

 (PI. LXXXIV, figs. 6, 7.) 



quaternarium Nordst. in Wittr. & Nordst. Alg. Exsic. 1880, 

 no. 383 ; fasc. 21, p. 40 ; ? Cooke, Brit. Desm. 1887, p. 102, t, 42, f . 5 ; 

 Nordst. Freshw. Alg. N. Zeal. 1888, p. 62, t. 7, f. 1 ; West, Alg. X. 

 Wales, 1890, p. 289 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 75. 

 Plcurotseniopsis quaternaria (Nordst.) De Toiii, Syll. Alg. 1889, p. 914. 



Cells of about medium size, a little longer than 

 broad, very deeply constricted, sinus narrowly linear 

 with a slio-htlv dilated extremity : semicells broadly 



O / / 



pyramidate-trapeziform with a subreniform base, basal 

 angles obtusely rounded, apical angles rounded, sides 

 slio-htlv convex and crenate-granulate (13-14 granules 



O t7 O O 



along each side), apex widely truncate and smooth ; 

 cell- wall granulate, granules rather small and disposed 

 in radiating series from the margin towards the centre, 

 in which there is a large subcircular- elliptic area 

 traversed by longitudinal and transverse granulate 

 ridges between which are conspicuous scrobiculations 

 (6 transverse and 9 longitudinal series of scrobicula- 

 tions). Side view of semicell circular. Vertical view 

 elliptic, margins granulate, granules most pronounced 

 at the middle on each side, granules within the margin 

 radiating from a smooth central area. Chloroplasts 

 consisting of 4 parietal plates in each semicell, each 

 with a single pyrenoid. 



Zygospore unknown. 



Length 68-72 p. ; breadth 58-65 ^ ; breadth of apex 

 about 26 IJL ; breadth of isthmus 20-24 //, ; thickness 

 38-40 p.. 



ENGLAND. - - Cocket Moss near Gig'gleswick, and 

 Baildon Moor, W. Yorks ! Cronkley Fell, N. Yorks ! 



WALES. Llyn Pad am, Carnarvonshire ! 



SCOTLAND.- -Achmacheen, Eoss ! 



Geogr. Distribution.- -Italy. Xew Zealand (var.). 

 Brazil. 



C. quaternarium is larger than C. margaritiferum, with a 

 much finer granulation and a different central area. Its 

 parietal cliloroplasts are also peculiar. 



