THE GREEN ALGAE OF NORTH AMERICA 163 



2. T. MUTICUM (A. Br.) Hansgirg, 1888, p. 131 ; Polyedrium 

 muticum A. Braun, 1855, p. 94; Reinsch, 1888, p. 498, PI. IV, 

 figs. 2, 4 and 6. Cells triangular, 13-28 /* diam., 7-10 //, thick ; 

 sides slightly sinuate, angles rounded, unarmed. Mass., 111., 

 Pa. Europe, Australia. 



The Mass, plant comes under forma majus Reinsch ; sides 

 slightly convex, angles rounded ; 23-28 /* diam., 10-11 p. thick ; 

 the 111. plant under forma punctulatum Reinsch ; sides slightly 

 concave, membrane finely punctate, diam. 18-21 /*. 



In general form and dimensions this species is much like 

 T. trigonum, but has more rounded angles and lacks the spine 

 or mucro characteristic of T, trigonum. 



3. T. TETRAGONUM (Nag.) Hansgirg, 1889, p. 18 ; Polye- 

 drium tetragonum Nageli, 1848, p. 84, PI. IV. B, fig. 2 ; Reinsch, 

 1888, p. 499, PI. IV, fig. 10 a and b; P. trigonum var. tetrago- 

 num Wolle, 1887, p. 184, PI. CLIX, figs. 7-10. Cells quad- 

 rangular, sides slightly sinuate, angles rounded. Diam. 15- 

 21 //.. Mass., 111., Pa., Neb. Europe, Australia, So. America. 



Characterized by the squarish outline, with rounded angles 

 and slightly concave sides, with no projections of any kind ; it 

 varies slightly as to dimensions, but not otherwise. 



4. T. MINIMUM (A. Br.) Hansgirg, 1888, p. 131 ; Wittr. and 

 Nordst., Alg. Exsicc., No. 1573; Polyedriiim minimum A. 

 Braun, 1855, p. 94; Reinsch, 1888, p. 499, PI. IV, fig. 2; 

 Wolle, 1887, p. 185, PI. CLIX, figs. 28-34. Cells quadrangu- 

 lar, 6- 1 1 /A diam., sides rather deeply emarginate, angles 

 rounded; in side view elliptic, 3-6 p. thick. Me., Pa. 



Europe, Asia, So, America. 



Resembles a small T. tetragonum, but according to Reinsch, 

 is not connected by intermediate forms. 



5. T. PQNCTULATUM (Reinsch) Hansgirg, 1889, p. 18 ; 

 Polyedrium punctulatum Reinsch, 1888, p. 500, PL IV, fig. 8. 

 Cells quadrangular, 18-21X21-30 //. ; in side view rhomboidal, 

 15-18 /A at the thickest ; sides straight or slightly and irregularly 

 repand, angles obtuse ; membrane thin, not lamellate, finely 

 granular-punctate. Mass. Europe. 



Our plant is forma rectangulare Reinsch, with cells longer 

 than wide. 



6. T. RETICULATUM (Reinsch) Hansgirg, 1889, p. 18 ; Polye- 

 dtiuin reticulatum Reinsch, 1888, p. 498, PL IV, fig. 3. Cells 

 triangular, 26-30 /u. diam. ; with equal and nearly straight sides, 



