8 



medio plus minus constrictum ; sinu acutangulo amplinto; semicellu- 

 lis subtriangularibus, lateribus rotundatis, dorso suhplanis, medio 

 convexis, subapice retusis, angulis acutis; a vertlce visis tri-vel tetra- 

 gonis; in forma trigona lateribus fere rectls; in forma tetragona re- 



n tt 



tusis, angulis acutis. Diam. .001 1 — .0013 



Hab. Nebraska Notch, Vt. "Collected by C. G. Pringle. 



The form nearest to this is St. Kjellmani, Wille, collected in Nova 

 Zembla, but it differs in size and in proportions of length to breadth; 

 in having the angles acute, not rounded, and turned upward in the 

 direction of the sides, not straight; in having triangular, not ellipti- 

 cal semicells; and in its back being straight, elevated in the centre, 



and retuse, not rounded. 



Staurastrum Donnellit, /?. sp. (Plate VI, Fig. \^.) St. par- 

 vum, duplo longius quam latins, oblongo-quadratum; cytiodermate 

 punctato et sulcato; semicellulis quadratis, angulis basalibus rotunda- 

 tis, lateribus leviter sinuato-retusis; angulis superioribus Tquatuor) in 

 cornu breve obtusum divergenter productis; a vertice visis, quadran- 

 gularibus. Diam. .0006". 

 Hab. Florida. Collected by Capt. John Donnell Smith- 



The form nearest this plant is St. pileolatum, Breb., but it differs 

 in having the ends furnished with three conical processes, and m 



being triangular in end-view. 



Staurastrum pentacladum, n. sp. (Plate VI, Fig. i6 and ida, 

 front and end views ) St. mediocre, granulato-asperum; semicellulis 

 ventre inflatis, dorso rotundatis, angulis in cornu apice distincte \n- 

 furcatum productis; a vertice visis quinque-radiatis; radiis substric- 

 tis, margine serrato-dentata. Diam. .0015". 



Jersey, J 



St. i^racilc, Ralfs, comes near this form, but its end-view is trira- 

 diate. ' N. Wille, of Norway, has published a variety, nanitm, which 

 is quadriradiate. ^ly plant has five arms, and the membrane is un- 

 usually rough; and, in addition, the points on the ends of the arms 

 are very prominent and divergent. 



Siaurastntm grallatorium, Nordst., var. ungulatum, n. var. 

 (Plate VI, Fig. 16.) Var. cornu in apicera aculeis smguhs curvatis, 



similibus aquilae ungulis producto. , „ * t>. m j 



Staurastrum crndaium, Wolle. (Plate VI, Fig. 18.) Described 



in Bulletin, Vol. VI., p. 123. a ^ 



Staurastrum Heleneanum, ;/. sp. (Plate VI, Figs 19 and 19^, 

 front and end views.; St. parvum, granulato-asperum; granulis in 

 series transversas ordinatis ; semicellulis subellipticis, dorso raodice 

 convexis, ventre tumidis; angulis in cornu productis; a vertice tri- 

 radiatis; radiorum basis inflatis, marginibus prommentibus apice 

 furcatis vestitis. Diam. .0012 — .0015 . 



Hab. Splitrock Pond, N. J., frequent. 1880. . 



There is a similarity between this desmid and St. vestitum. Raits; 



but, while the latter has two slender forked spines at the middle of 



each side, mine has stouter forked processes on the inflated base of 



each arm; and, in addition to this, the plant is only about half the 



size of St. vestituin. 



Euastrum attenuatum, «. sp. (Plate VI, Fig. 20, front view; 



