THE GREEN ALGAE OF NORTH AMERICA 165 



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

 Mass. I Europe. 



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

 forma leptodcrmum ; both forms have cells 17-19 p- diarn., 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. REGULARS Kiitzing, 1845, p. 129; Polyedrium tetrae- 

 dn'ciim Niigeli, 1848, p. 84, PL IV. B, fig. 3. Cells tetraedric, 

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

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

 lamellate. 



Many varieties and forms have been described ; we have only 

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

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

 ra ; 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 CLJX, figs. 11-14; P. tumidulum 

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

 irregularly 5-6-angled, 65-75X35-45 M. sides concave, angles 

 unarmed. Me., Mass., Pa. 1 tin-ope. 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 //. diam., with irregular, rounded sides, and 3 or 4 incon- 

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

 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 /x diam., flattened, with 3 nearly 

 straight sides, and 2 spines at each angle. 



15. T. BIFURCATUM (Wille) Lagerheim, i893a, p. 160 ; 

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

 CL1X, figs. 15-18. Cells tetraedric, about 30 /* diam., 3 or 4- 

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



So. America. 



16. T. ENORME (Ralfs) Hansgirg, 1888, p. 132; Polyedrium 

 enonnc Wolle, 1887, p. 184, PL CLJX, figs. 19-23. Cells irreg- 

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

 colorless, often deeply lobed, sometimes repeatedly forked ; 

 divisions mucronate. Me., Pa. hurope. 



With many varieties and forms, based on dimensions and on 



