FRESH -WATER A L G .E OP THE UNITED STATES. I57 



Ilab. — America ; Ehrcubcrg. 



Frond in front view broader than long; constriction deep, acute not linear; segments subcllii)- 

 tic, sometimes irregular spines subulate, geminate, marginal, central protuberance cylindrical, 

 truncate border minutely dentate. L. (not including spines) 5^5^". B. 5J5" to ^^j". 



X. criiiitatuni, Breb. 



X. parFum, la;ve ; semicellulis subhaemispherico-reniformibus, utroque polo aculeo uuico in- 

 curvo, ambitu aculeis octo geminatis, a dorso ovato-ellipticis, utroque polo aculeis teriiis, in 

 medio plerumque aculeo abbreviato. (R.) Species mihi ignola. 



X»«am.— 0.00196". R. 



Syn. — X criaiatum, Brebisson. Ralfs, British Dcsmidiete, et Rabeniiorst, Flora Europ. 

 Algarum, Sect. III. p. 224. 



ITah. — South Carolina ; Georgia ; Florida ; Bailey. 



Frond rather longer than broad; constriction deep, linear ; segments subreniforra or truncate 

 at ends ; spines straight or curved, subulate, marginal, one at each side, at the base of the 

 segment, solitary, the others geminate, in four pairs ; central protuberance short, conical. (A.) 



X. coronatiiui, Ehrb. 



X. semicellulis subglobosis binis, aculeatis, ubique asperis, aculeis crassis apiee truncatis triden- 

 tato-coronatis quatuor utrinquc dorsalibus, uno utrinquc latere medio. (R.) Species mihi 

 ignota. 



Syn. — X. coronaium, Ehrenbero, Yerbreitung, p. 138, et Rabenhorst, Flora Europ. Alga- 

 rum, Sect. III. p. 224. 

 Asteroxanthium coronatum, KIjtzing. Rabenhorst, {loc. cit.) 



Hab. — America ; Ehrenbcrg. 



Rcmarh. — Mr. Archer appears to think that this species is simply a form of 

 Staurastrum furcigerum. (Breb.); see Pritcliard's Infusoria, p. 743. 



X. fasciciiIntiiiH, Eurb. 



X. parvum, singulum, constrietionc profundo linear! ; cytioderraate Isevi vel subla;vi ; semicel- 

 lulis oblongo-reniformibus vol hcxagonis, diametro duplo longioribus, ambitu aculeis gracilil)us 

 geminatis 4-6, a dorso ellipticis, utroque polo aculeis quatuor instructis. (R.) Sp>ecies mihi 

 ignota. 



Z)iani.—0.0022S"— 0.00256". (R.) 



Syn. — X /ascicuZo/um, EHRENBERa. Rabeniiorst, Flora Europ. Algarum, Sect. III. p. 223. 



Sab. — South Carolina ; Georgia; Florida; Rhode Island ; Bailey. 



Frond about as long as broad; constriction deep, linear; segments somewhat reniform or sub- 

 hexagonal, twice as broad as long, spines slender, subulate geminate, marginal, in four or six 

 pairs ; central protuberance short, conical, somewhat truncate. (A.) 



Genus ARTHRODESMUS, Ehrb. 



Celluhe profunde constricts ; semicellukc compressa; aut oblong.x, utroque polo aculeo subulate 

 firmo instructiB, aut quadraugulares, angulis in aculeum rectum vel curvum productis, a dorso vel 

 ellipticae vel fusiformes. Massa chloropbyllacea in fascias quatuor radiantes disposita. (R.) 



Cells profoundly constricted ; semicells compressed or oblong, furnished at each end with a subu- 

 late spine, or else quadrangular with the angles produced into straight or curved spines, the dorsal 

 aspect, elliptic or fusiform. Chlorophyl masses disposed in four radiating fascia. 



