156 FIIESH-WATER ALGJE OF THE UNITED STATES. 



Cells single or geminately concatenate, inflated, profoundly constricted ; semicells compressed, 

 oblong, hemispherical or subquadrangular, protruding in the centre as a rounded truncate or den- 

 ticulate tubercle Cytioderni firm, armed with sets, or simple, or bi- tri-furcately divided spines. 

 C'hlorophyl radiately expanded. Zygospores armed. 



Eenuxrlc. — It has so happened that I have identified but a single species of this 

 genus. 



3l. aciileatiim, Eiirb. 



X. parvum, singulum, sparsum, diaraetro ipse subnequale, ex obliquo ellipsoideum, diametro 

 duplo longius, coustrictione obtusa lineari, semicellulis oblongis subreniformibus, basi sub- 

 plauis, dorso late rotundatis, tuberculo centrali minus elevato, truncate, niargine autem crenato- 

 dentato ; cytiodermate undique aculeis subulatis obsito. (R.) Species mihi ignota. 



Dmm.— (Sine aculeis) 0.0025"— 0.0029". (R.) 



Syn. — Xanthidiuvi aculeatum, Ehrenberg. Rabenhorst, Flora Europ. Algarum, Sect. III. 

 p. 222. 



Sab. — Prope Savannah, Georgia ; Railey. 



Frond inf. v. broader than long; constriction deep, linear; segments somewhat reniform; 

 spines subulate, short, scattered, chiefly marginal ; central protuberance cylindrical, truncate, 

 border minutely dentate. (A.) 



X. Arctiscon, Eiirb. 



X. semicellulis globosis, binis, aculeatis, aculeis numerosis undique sparsis crassis asperis apice 

 trilobis. (R.) Sj^ccies mihi ignota. 



Syn. — X Arctiscon, Ehrenbero. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 224. 



Hab. — America borealis ; Ehrenberg. 



Frond in f. v. about as long as broad ; constriction forming a wide notch ; segments narrowed 

 at the base, with broadly rounded ends; spines numerous, restricted to the outer margin, 

 scattered, elongate, stout, terminated by three or four diverging points. (Archer.) 



X. arniatiim, (Breb.) Ralfs. 



X. maximum, validum, solitarium vel binatim conjunctura, diametro plerumque duplo longius; 

 semicellulis subcordatis vel angulari-rotundatis tuberculo centrali subelevato, truucato, mar- 

 gine granulato-dentato prasditis ; cytiodermate verruculoso et processibus stepius geminatis 

 truncatis apice inciso-furcatis instructo. (R.) 



Syn. — Xanthidium armalum, (Brebisson) Ralfs, British Desmidieaj et Rabenhorst, Flora 

 Europ. Algarum, Sect. III. p. 222. 



Sa6.— South Carolina ; Florida ; Bailey. Saco Lake ; (Lewis) Wood. 



Frond large, in f. v. twice as long as broad ; constriction deep, linear ; segments broadest at 

 the base; ends rounded or somewhat truncate; spines in pairs, principally marginal, short, 

 stout, terminated by three or four divergent points ; central projections cylindrical trnncate, 

 the border dentate ; e. f. punctate. Sporangium large, orbicular, with depressed tubercles, 

 perhaps immature. L. jIj;". B. jf^". (A.) 



Remar7c.—¥ig. 17, pi. 13, is a front view of a frond, magnified 260 diameters. 



X. bii^enai'iuin, Ehrb. 



X. semicellulis globosis subangulosis, binis, aculeatis ; aculeis fasciculatis, fasciculis in quovis 

 globulo senis. Species mihi ignota. 



Syn.—X. hisetmrium, Ehrenberg. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 224. 

 X. Bribissonii, Ralfs. Archer, Pritohard's Infusoria, p. T3G. 



