COSMAKIUM. 203 



C. margaritiferum only in its slightly more rounded semicells, 

 and in the greater localization of the central scrobiculations 

 combined with the slight differentiation of the central granules. 

 These three forms can be summarized as follows :- 



Forma confusa. 



Cosmarium Brebissonii Menegli. a genuina Jacobs. Desm. Daiiem. 1876, 

 p. 194, t. 7, f. 15 (forma latior et forma ang-ustior) ; Arcli. in Micr. 

 Journ. 1877, xviii, p. 305. 



C. confusum Cooke, Brit. Desm. 1887, p. 110, t. 42, f. 9 ; De Toiii, Syll. 

 Alg. 1889, p. 995. 



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



Basal angles of semicells furnished with a somewhat 



o 



elongated conical granule. 



Recorded from Ireland bv Archer. 



/ 



Forma regularior. 



Cosmarium confusum Cooke var. regularius Xordst. iu Bot. Xotiser, 1887, 

 p. 159 ; FresW. Alg-. X. Zeal. 1888, p. 47, t. 5, f. 6. 



Apex of semicells furnished witli a few granules ; 

 granules as a whole slightly smaller than in the type. 



Length 4453 ^ ; breadth 35-41 ^ ; breadth of 

 isthmus 13-15 JJL ; thickness 26 p.. (PL LXXXII1, 



%. 12.) 



Very uncommon,, but probably widely distributed. 



Forma Kirchneri. 



Cosmarium trachypleurum Lund. var. rerrucosum Kirclin. Alg\ Schles. 



1878, p. 152. 

 C. subtholi forme Eacib. var. verrv.cosum (Kirclin.) Eacib. Xonii. Desm. 



Polon. 1885, p. 7(3. 

 C. Kirchneri Borg. Bidrag Bornh. Desm.-fl. 1889, p. 143, t. 6, f . 3 ; 



Anderss. Sverig. Chlor. 1890, p. 17 ; Borge, Siissw. Chlor. Archang. 



1894, p. 29 ; Borg-. Ferskv. Alg. Ostgronl. 1894, p. 12 ; Xordst. Index 



Desm. 1896, p. 151 ; Borg. Freshw. Alg. Faeroes, 1801, p. 227. 



Semicells with the apical angles more rounded, with 

 a slight differentiation of granules in the centre and 



o o 



the localization of the minute scrobiculations to this 

 small area. 



Length 52-60 ^ ; breadth 44-52 p. ; breadth of 

 isthmus 13-18/x.; thickness 37 /*. (PI. LXXXIII, 



fig- 13.) 



This form has not yet been observed in the British Islands. 



