FRESII-WATER ALG^ OF THE UNITED STATES. I49 



Hah. — South Carolina ; (Tlavenel) Wood. 



Smootb, small; sinus ample, obtuse auglcd (sometimes acute angled?); seniicclls elliptic (or 

 subtriangular ?), 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. 



RemarTcs. — This species was collected near Aiken, Sonth 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 in 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. ariistiieruni, Ralfs. 



St. Iseve, St. cuspidatum quodaramodo simile, et eadem magnitudine sed isthnio destitutura ; 

 semieellulis tumidis, in media parte subi-otundatis, lateraliter in lobum, basi constrietum, 

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

 iEquidistantibus cruciatim dispositis, iuterstitiis profuude exeisis. (R.) Species mihi ignota. 



Diam.—lnc\. arist. 0.0014". (R ) 



Syn. — St.aristiferum, Ralfs, British Desmidieae, p. 123. Rabenhorst, Flora Europ. Algarum, 

 Sect. III. p. 204. 



Hah. — Georgia ; Rhode Island ; Bailey. 



Segments smooth, in f v. prolonged at each lateral extremity into a mamillate 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. liCwisii, Wood. 



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

 eellulis a fronte late triangularibus, a vertice triangularibus et cum angulis uonnihil tumidis, 

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



Diam. — Long. cum. spin, -j^^" = .0025"; lat. cnm. spin. tuVjtV = .00225". Sine spin. : long, 

 gij" = .001666"; lat. t^'oW .001660". Spin.: long. -J^/ = .000066" 



Syn. — St. Lewisii, Wood, Proc. Acad. N. S. 1870. 



ffab. — In lacu Saco; (Lewis) Wood. 



Smooth, with a very ample sinus, which is armed with a small spine and ha.s a very obtuse 

 angle; isthmus absent; scmicells 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. 



Remarks. — This desmid is most closely allied to St. aristifenim, 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. 



