256 BRITISH DESM1DIACE.E. 



This small species is exceedingly characteristic by reason 

 of the three equal crenations at each side of the semicells and 

 the two small ones in the middle of each apex. The basal 

 crenations are trigranulate, but the rest are bigranulate ; and 

 rhe central tumour is furnished with a ring of 7 or 8 granules 

 surrounding a single central granule. The chloroplast con- 

 tains one large central pyrenoid. 



We have in the past confused this species with C. alatum 

 Kirchn., largely owing to the imperfect description and 

 absence of figures of the latter. Dr. 0. Ivirchner has,, how- 

 ever, very kindly placed in our hands his original figure of 

 C. alatum, and there can be no longer any question of the 

 specific distinction of C. subalatum. 



Although C. alatum is not British we append a description, 

 and also give figures, not merely of the type, but of a tropical 

 variety of it. We hope by this means to finally clear up 

 any doubt concerning Kirchner's C. alatum and its relations 

 with C. subalatum. 



Description of C. alatum Ivirchner : 



COSMAEIUM ALATUM Kirchiier, Alo\ Schles. 1878, p. 153 ; De 

 Toni, Syll. Alg. 1889, p. 1021 ; Nordst. Index Desm. 1896, 

 p. 41. C. alatum a. silesiacum Eacib. Nonn. Desm. Polon. 

 1885, p. 73. Ursinella alata Kuntze, Revis. gen. plant. 1891, 

 ]). 924. Cells small, about 14- times as long as broad, deeply 

 constricted, sinus narrowly linear ; semicells subpyramidate- 

 trapeziform, with a broad flat base and a rather narrow apex, 

 lateral margins rather markedly biundulate (with two hollows 

 and a median crest), basal and apical angles rounded, apex 

 slightly retuse ; cell-wall granulate, granules with no definite 

 radial arrangement,, about 3-4 showing at the margin of each 

 ]obe of the semicell ; in the centre with a granulate pro- 

 tuberance. Vertical view elliptic, with a large rounded pro- 

 tuberance at the middle 011 each side. Chlorplasts axile, each 

 with two pyrenoids. Zygospore unknown. Length about 

 46 ju ; breadth about 37 JJL ; breadth of isthmus 11 /n : thickness 

 24 ji. (PL XC, fig. 11.) 



Geogr. Distribution. Germany. Poland (var.). Ecuador 

 (var.). 



C. alatum differs from C. subalatum in its larger size, its 

 sinuate rather than crenate margins, its relatively narrower 

 and retuse (not crenate) apex, its more numerous and less 

 regularly arranged granules, its larger, more granulated 

 central tumour, and in the possession of two pyrenoids in each 

 chloroplast. 



