45 



a very strongly dilated apex ; semicells subsemicircular, 

 basal angles snbrectangular and slightly rounded, apex 

 very slightly flattened. Cell- wall granulate ; grannies 

 rather distant and arranged in somewhat irregular 

 oblique series, slightly diminishing in size towards the 

 centre of each semicell ; above the isthmus with 3 

 rather irregular transverse series of small granules, 

 about o or 6 in each series ; between the granules 

 minutely and densely punctate. Side view of semi- 

 cell circular. Vertical view elliptic with rounded 

 poles, ratio of axes 1 : 1*5. 



Zygospore unknown. 



Length 79 p.; breadth 65 /x; breadth of isthmus- 

 17 jic ; thickness 3D p.. 



ENGLAND.- -Chippenham Fen, Cambridgeshire ! 



This species has the same outward form as C. radiosum 

 AVolle, but is otherwise very different from it. It should he 

 compared with C. dentiferum Corda, and with forms of C. 

 marguritiferum. 



250. Cosmarium taxichondrum Lund. 

 (PL CIII, figs. 11-13). 



Cosmarium taxichondrum Ltind. Desm. Suec. 1871, p. 39, t. 2, f. 13 ; "VVille. 



Norges Ferskv. Alg. 1880, p. 32; Wolle, Desm. U. S. 1884, p. 71, t. 16, f. 



32-34; Lagerh. Bidr. Amerik. Desm.-fl. 1886, p. 237; Haiisg. Prodr. 



Algenfl. Bohm. 1888, p. 197 ; De Toni, Syll. Alg. 1889, p. 990 ; Borge, 



Siissw. Chlor. Archang. 1894, p. 31 ; W. & G. S. West, Alg. Madag. 1895, 



p. 66, t. 7, f . 2 ; Nordst. Index Desmid. 1896, p. 250 ; Cushman in Bull. 



Torr. Bot. Club, xxxii, 1905, p. 551 ; Borge, Beitrage Alg. Schwedeii, 



1906, p. 42. 



C. taxichondrum a genuina Racib. Desm. Xowje, 1889, p. 88. 

 Ursinella taxichondra Kuntze, Revis. gen. plant. 1891, p. 925. 



Cells rather small, a little longer than broad, very 

 deeply constricted, sinus linear and slightly undulated ; 

 semicells semicircular, with the basal angles slightly 

 thickened and giving a faint impression of being* 

 directed downwards, apex slightly flattened or sub- 

 truncate ; cell-wall punctate, furnished with a prominent 

 granule in the median part of the semicell immediately 

 above the isthmus, and with two transverse arcuate 

 series of granules in the upper median region of the 



