FRESH-WATER ALGiB OF THE UNITED STATES. 149 



Hah. — South Carolina ; (Ravenel) Wood. 



Smooth, small ; sinus ample, obtuse angled (sometimes acute angled ?) ; semicells elliptic (or 

 subtriangular ?J, with the dorsum slightly convex, at the angles with a straight or curved 

 transparent spine ; from the vertex triangular (or quadrangular ?), angles often rounded, 

 with a sometimes obsolete spine superimposed. 



Remarhs. — This species was collected near Aiken, South Carolina, by Prof. 

 Ravenel, who found it forming with various diatoms and desmids a slimy mass in 

 a feebly running ditch. It agrees very well with the European form, except that 

 it is not so large (at least the largest I ever measured did not come up to the 

 size of their transatlantic brethren), neither does it appear to vary quite so much. 

 In the description, I have placed in brackets those characters ia which the European 

 form varies, and the specimens I have seen do not. 



Fig. 18, pi. 21, represents outline of end of a semicell, magnified 750 diameters. 

 Fig. 9, pi. 13, a front view, and 9 a the end view, of the living frond, magnified 

 diameters. 



St. aristiftruni, Ralfs. 



St. lasve, St. cuspidatura quodammodo simile, et eadem magnitudine sed isthmo destitutum ; 

 semicellulis tumidis, in media parte subrotundatis, lateraliter in lobnm, basi constrictum, 

 apice aristatum productis, lobis divergentibus, a vertice tri-quadrilobo-radiatis, radiis strictis 

 sequidistantibus eruciatim dispositis, interstitiis profunde excisis. (R.) Species mihi ignota. 



Dmm.— Incl. arist. 0.0014". (R.) 



Syn. — St.aristiferum, Ralfs, British Desmidiese, p. 123. Rabenhokst, Flora Europ. Algarum, 

 Sect. III. p. 204. 



HaJ). — Georgia ; Rhode Island ; Bailey. 



Segments smooth, in f. v. prolonged at each lateral extremity into amamillate projection, which 

 is terminated by a subulate, acute straight awn, the awns divergent, e. v. with three or four 

 angles ; angles inflated mamillate, terminated by an awn, sides deeply concave in the centre. 

 (A.) 



St. liewisii, Wood. 



St. laeve ; sinu amplissimo, spinulo parvo armato et cum angulo obtuso ; isthmo nullo ; semi- 

 cellulis a fronte late triangularibus, a vertice triangularibus et cum angulis nonnihil tumidis, 

 et rotundatis ; angulis spino maximo, robusto, acuto armatis. 



Diam. — Long. cum. spin..^^^" = .0025" ; lat. cum. spin. x^^W' = -00225". Sine spin. : long. 

 ^U' = -001666" ; lat. tuVW -001666". Spin. : long. ^^Vrr" = -000666" 



Syn. — St. Lewisii, Wood, Proc. Acad. N. S. 1810. 



Hah. — In lacu Saco ; (Lewis) Wood. 



Smooth, with a very ample sinus, which is armed with a small spine and has a very obtuse 

 angle ; isthmus absent ; semicells from the front broadly triangular, from the vertex trian- 

 gular, with the angles somewhat tumid and rounded ; angles armed with a very large acute 

 robust spine. 



BemarTcs. — This desmid is most closely allied to St. aristi/erum, Ralfs, but differs 

 from it in outline as seen from the front, there being no mamellation of the ends. 

 The spines in the sinuses are always wanting in the European species. 



Fig. 19, pi. 21, represents the outline of the end of a semicell, magnified 750 

 diameters.. Fig. 11, pi. 13, represents the perfectly formed frond, magnified 750 

 diameters. 



