COSMAKIUM. 239 



Semicells rather more elevated ; granules of the 

 central tumour variable (as in the type) but with a 

 more definite concentric disposition. Chloroplasts 

 with one pyrenoid. 



Length 22-29 /x ; breadth 18-25 /i; breadth of 

 isthmus 5'4-6'6 ^ ; thickness 14'5-15'4/x. 



ENGLAND. G-uvhirne, Cambridgeshire ! 



/ ' O 



Geogr. Distribution. Bosnia. 



This form is scarce!}* to be separated from typical C. snb- 

 costatum, as the granulation of the central tumour varies in 

 this, as in other species,, to a considerable extent. 



The form of C. subcostatum figured by Schmidle (in 'Ber. 

 Deutsch. Botan. Ges.' x, 1892, t. II, f. 12) is particularly 

 interesting as it possesses the same form of semicell as 

 Gutwinski's " C, Beckii ' combined with a central tumour 

 much more nearly approaching that of C. subcostatum. 



The larger forms of C. subcostatum appear to possess two 

 pyrenoids in each chloroplast, but the smaller forms only one. 



205. Cosmarium costatum Xordst. 

 (PL LXXXVII, figs. 13-16.) 



Cosmarium crenatum Ralfs subsp. costatum Xordst. Desm. Spetsb. 1872, 



p. 30, t. 6, f. 9. 

 C. costatum Nordst. Desm. Arctose, 1875, p. 25, t. 7, f. 17 ; Boldt, Desni. 



Groiiland, 1888, p. 21 ; De Toni, Syll. Alg. 1889, p. 1012 ; Eoy & Biss. 



Scott. Desm. 1894, p. 44 ; Schmidle, Lappmark Stisswasseralgen, 1898, 



p. 38, t. 1, f. 57, 59 [forma] ; G-. S. West, Alga-fl. Cambr. 1899,' p. 218 ; 



Borge, Susswasseralgen Franz Josefs-land, 1899, p. 763 ; West & G. S. 



West, Notes Alg. Ill, 1903, p. 75 ; Larsen, Freshw. Alg. E. Greenland, 



1904, p. 84; West & G. S. West, Freshw. Alg. Orkneys and Shetlands, 



1905, p. 21. 



Ursinella costata Kuntze, Revis. gen. plant. 1891, p. 924. 



Cells somewhat small, 1-t- 1 J times as long as broad, 

 fairly deeply constricted, sinus narrowly linear ; semi- 

 cells snbtrapeziform, lower portion of equal width, 

 upper portion some upwardly attenuated, basal angles 

 rectangular, sides incised-crenate, crenations 4-5, one 

 or two small and entire at the basal angles, the others 

 emarginate, apex truncate and 4-crenate (including the 

 apical angles), crenations emarginate; with minute 

 granules disposed in radiating and concentric series 

 within the margin, granules bin ate except the inner- 



