THE GREEN ALGAE OP NORTH AMERICA 165 



elliptic ; membrane very thick, up to 5 //., of 2-many lamellae. 

 Mass. Europe, 



The type is not reported with us, but only forma minus and 

 forma leptodermum ; both forms have cells 17-19/0. diani., mem- 

 brane thinner and less lamellate than in the type ; from Reinsch's 

 description and figures it is not easy to find any distinction be- 

 tween the two forms. 



12. T. REGULARE Kiitzing, 1845, p. 129; Polyedrium tetrae- 

 dricum Nageli, 1848, p. 84, PI. IV. B, fig. 3. Cells tetraedric, 

 usually 14-50 /u, diam., sides plane or slightly concave, angles 

 obtuse, each with a short spine ; membrane thick, distinctly 

 lamellate. 



Many varieties and forms have been described ; w 7 e have only 

 var. longispinum (Reinsch) De Toni, 1889, p. 605 ; Polyedrium 

 tetraedricum var. longispinum Reinsch, 1888, p. 506, PL V, fig. 

 la ; P. B.-A., No. 1466. Spines longer, up to half the length 

 of a side. Mass. Europe. 



13. T. GIGAS (Wittr.) Hansgirg, 1888, p. 131 ; Polyedrium 

 gigas Wolle, 1887, p. 184, PL CL,IX, figs. 11-14; P- tumidulum 

 var. rotundatum Reinsch, 1888, p. 506, PL VI, fig. 3a. Cells 

 irregularly 5-6-angled, 65-75X35-45 /", sides concave, angles 

 unarmed. Me., Mass., Pa. Europe, New Zealand. 



14. T. ARMATUM (Reinsch) De Toni, 1889, p. 611; Polye- 

 drium armatum Reinsch, 1888, p. 508, PL VI, fig. i. Cells 

 22-31 /u, diam., with irregular, rounded sides, and 3 or 4 incon- 

 spicuous rounded angles, each with i or 2 stout spines, 5-8 //, 

 long ; membrane rather thick, not lamellate. Mass. Europe. 



Beside the type we have var. minus Reinsch, 1888, p. 508, 

 PL VI, fig. ic ; Cells 22 /j. diam., flattened, with 3 nearly 

 straight sides, and 2 spines at each angle. 



15. T. BIFURCATUM (Wille) L/agerheim, i893a, p. 160 ; 

 Polyedrium trigonum var. bifurcatum Wolle, 1887, p. 184, PL 

 CLIX, figs. 15-18. Cells tetraedric, about 30 p. diam., 3 or 4- 

 angled, angles bifurcate, with sharp tips. Cuba, Porto Rico. 



So. America. 



16. T. ENORME (Rail's) Hansgirg, 1888, p. 132; Polyedrium 

 enormeWolle, 1887, p. 184, PL CLIX, figs. 19-23. Cells irreg- 

 ularly tetraedrical, generally 25-45 /x, diam., angles prolonged, 

 colorless, often deeply lobed, sometimes repeatedly forked : 

 divisions mucronate. Me., Pa. Europe. 



With many varieties and forms, based on dimensions and on 



