COSMARIUM. 243 



bigranulate crenations on the lateral margins, and the 

 granules of the central tumour are stronger; but the general 

 characters and the disposition of the granules are precisely 

 the same. 



207. Cosmarium subreniforme Xorclst. 

 (PI. LXXXVIII, fig. 6.) 



Cosmarium subreniforme Xorclst. Desm. Arctoae, 1875, p. 24, t. 7, f. 16 ; 

 Boldt, Sibir. Chlorophy. 1885, p. 105 ; De Toni, Syll. Alg. 1889, p. 1050 ; 

 Xorclst. Index Desni. 1896, p. 247 ; Borge, Stisswasseralgen. Franz Josefs- 

 land, 1899, p. 763 forma: ; West & G. S. West, Alga-fl. Yorks. 1901, 

 p. 220; Borge, Beitrage Alg. Schweden, 1906, p. 41, t. 2, f. 30 [forma]. 



I'rsinella siibreniformis Kiintze, Revis. gen. plant. 1891, p. 925. 



Cells rather small, slightly longer than broad, deeply 

 constricted, sinus narrowly linear with a widely dilated 

 extremity ; semicells reniform with a truncate apex, 

 lateral margins 7-8-crenulate (due to small granules), 

 apex straight and indistinctly 4-5-crenulate, within 

 the margin with a number of minute granules more or 

 less irregularly disposed, in the centre above the 

 isthmus with a tumour furnished with 5 vertical series 

 of granules. Side view of semicell very broadly sub- 

 ovate, with a somewhat flattened apex. Vertical view 

 rather narrowly elliptic, granulate, granules disposed 

 in curved transverse series, absent in the centre, with 

 a broad granulate tumour at the middle on each side. 



Zygospore unknown. 



Length 36-3 7 /x; breadth 31-33 //,; breadth of 

 isthmus 10-11 p,; breadth of apex 13-14 /x; thick- 

 ness 22 p.. 



EXGLAXD.- -Strensall Common, X. Yorks ! 



Geogr. Distribution. Poland. Sweden. Franz 

 Joseph Land. Spitzbergen. Siberia. 



This rare species is distinguished from C. subcrenatum by 

 its granulate (and not crenate) margin and by the different 

 disposition of the granules, which are never arranged in pairs. 

 It should also be compared with C. 8porttlla, from which it 

 differs in its unproduced and undilated apex, and in its central 

 tumour. It differs from C. onudnin in the form of its semi- 

 cells, with a higher apex although not produced, in its much 

 smaller granules, and in the nature of its central tumour. 



