158 F RES II -WATER A L G .E OF THE UNITED STATES. 



licmarj.-s.—l have found only a single iindesrrilxHl species of tliis genus, Lut the 

 following Euroi)eaii forms have been detected in this country by Prof. Bailey. The 

 genus appears to be, as Prof. Ilabcnhorst says, scarcely distinguishable from Xan- 

 thidium or Slaarastrum. 



A. octocorniM, EaiiB. 



A. parvus, lasvis, constrictionc lata cxcavata; semicellulis trapezoideis, inciso-qnadriradiatis, 

 radiis in aculeura acutissimum strictura porrectis, a latere elongato-ellipticis, diametro fere 

 triple longiorilius, utroquo polo aculeum singulum gerentibus. (R.) 



j;/a,n.— O.OOOnu". (R.) 



<iyn. XanthiJiuiii ocfucoriie, Ralfs. Bailey, Microscopical Observations, p. 29. 



Arlhrode^inus octocornis, Ehrenberg. Rabenhorst, Flora Europ. Algarum, Sect. III. 

 p. 223. 



ITab. — Florida ; Rhode Island ; Bailey. 



Frond smooth, iiiimito, about as long as broad; constriction a wide notch; segments much 

 compressed, trapezoid, each angle terminated by one or two straight, subulate, acute spines, 

 the intervals between the angles concave. (A.) 



a. Spine solitary at each angle. L. tj^t"- B. tsVs"- (■'^■) 



h. Larger spines geminate at each angle. L. toVij"- !>• sW- ('^) 



A. quadridens, Wood. 



A. late ovalis, vel suborbicularis, paulum longior quara latus, cum raargine crenato-nndulato; 

 se.raicellulis nonnibil reniformibus, utroque fine aeuleo subulato, modice robusto, acuto, re- 

 curve, armatis; cytiodermate cum verruculis paucibus modice minutis in seriebus paucibus 

 dispositis instructo; semicellulis a vcrtice acute ellipticis, ct cum margine crcnato ct super- 

 ficie sparse vcrruculosa. 



l>iam.—Uit. jij^uij" = .00075" ; long, j/^/ = .00125". 



Sijn. — A. quadridens, Wood, Proc. A. N. S. 18C9. 



Hab. — lu laeu Saco, (Lewis) Wood. 



Broadly oval or suborbicular, a little longer than broad, with the margin crenately undulate; 

 semicells somewhat reniforra, at each end armed with a subulate, moderately robust, acute, 

 recurved large spine ; cytiodcrm with a few smallish tubercles arranged in three or four rows ; 

 semicells from the vertex acutely elliptical, with the margin creuate and the surface sparsely 

 warty. 



Remarks. — This species approximates .1. dlccrgcns, from which it differs in tlie 

 arrangement of its granules, its attaining not one-half the size, and, I believe, iu 

 the larger and more robust spines. 



Fig. 2, pi. 20, represents an empty frond of this species. 



A.Incu§, (Breb.) Hassal. 



A. parvus tarn longus quam latus, constrictionc lineari obtusa vel late excisa; semicellulis 

 oblongo-quadrangularibus, angulis externis aculeatis, interuis rotundatis iucrmibus, aculeis 

 longis singulis divergentibus. (R.) 



Dmw.— Max. 0.00098". Long. 0.00091". Spor. (sine acul.) 0.00085". 



Si/n.—A. Incus, (Brebisson) IIassal, Fresh-Water Algii;, p. 357, ct Rabenhorst, Flora 



Europ. Algarum, Sect. III. p. 22G. 

 7/a6.— Georgia; Florida; South Carolina ; Rhode Island ; Bailey. 



Frond minute, smooth, as long, or longer than broad, constrictions a deep notch or sinus; seg- 

 ments with inner margin turgid, outer truncate ; spines subulate, acute ; sporangium orbii-uhir, 

 spinous; sjiincs subulate. (Archer) 



