156 FRESH-WATER ALG^E 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 Cytioderm firm, armed with setae, or simple, or bi- tri-furcately divided spines. 

 Chlorophyl radiately expanded. Zygospores armed. 



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

 genus. 



X. aculeatum, EHRB. 



X. parvum, singulum, sparsum, diametro ipse subtequale, ex obliquo ellipsoideum, diametro 

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

 planis, dorso late rotundatis, tuberculo centrali minus elevato, truncate, marginc autem crenato- 

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



Diam (Sine aculeis) 0.0025" 0.0029". (R.) 



Syn. Xanihidium aculeatum, EHRENBERG. RABEMIIORST, Flora Europ. Algarum, Sect. III. 

 p. 222. 



Hab. Prope Savannah, Georgia ; Bailey. 



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, EHRB. 



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

 trilobis. (R.) Species mihi ignota. 



Syn. X. Arctiscon, EHRENBERG. 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.) 



AL, a mint ii HI, (BREB.) RALFS. 



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

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

 gine granulato-dentato prseditis ; cytiodermate verruculoso et processibus saspius geminatis 

 truncatis apice inciso-furcatis instructo. (R.) 



Syn. Xanihidium armatum, (BREBISSON) RALFS, British Desmidieaa et RABENHORST, Flora 

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



Hab. 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 truncate, 

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

 perhaps immature. L. T | T ". B. ^ v ". (A.) 



Remark. Fig. 17, pi. 13, is a front view of a frond, magnified 260 diameters. 



X. bixciiariiim, EHRB. 



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

 globulo senis. Species mihi ignota. 



Syn. X. bisenarium, EHRENBERG. RABENHORST, Flora Europ. Algarum, Sect. III. p. 224. 

 X. Brebissonii, RALFS. ARCHER, PRITCHARD'S Infusoria, p. 736. 



