32 THE FLORA OF NEBRASKA. 



Yah. -tetragonum Rabh.— Pour-angled, one or rarely two or more mucrons at 

 each angle. PL IV., Fig. 4. 



Var. — pniictatiim Kirch. — Four-angled, each angle with a short obtuse process; 

 membrane finely granular; diameter of cells 13-36 //. 



Var.— mill ns Reinsch Algenfl. Frank, tab. III. PI. IV, Fig. 2. — Sides concave, much 

 smaller. 

 Standing water, Lincoln. 



Tetraedon loiigispimim (Perty) Hansg. Hedwigia, 1888, 132. 

 Cerasterias longispina (Perty) Reinsch Notarisia 1888, 572. 



Four-radiate; radii thin, elongated, scarcely thickened in the center; length 



of radii 35-50 u. 

 Stagnant ponds, Lincoln. PI. IV, Fig. 3. 



Tetraedon raphidioides (Reinsch) Hansg. Hedwigia, 1888, p. 131. 

 Cerasterias raphidioides Reinsch Algenfl. Frank. 68. 1867. 

 Polyedrium reinschii Rabh. Fl. Eur. Alg. III., 62. 1868. 



Three to eight radiate; radii subulate, acute or obtuse. 



In stagnant water, Lincoln. 



5. RAPHIDIUM Kuetz. Phycol. Germ. 144. 1845. 



Cells fusiform or cylindrical, usually cuspidate or acuminate at the end, or 

 rarely obtuse, straight or curved, single or aggregated; contents green, 

 slightly granular, furnished with a central or rarely lateral, transparent 

 vacuole; propagation by division of cells in one direction, zoogonidia 

 unknown. 

 Etymology: Greek pa<ptc, needle. 



Raphidinm polymorphnm Fresen, in Abhandl. der Senckenb. Naturf. Ges. 

 II., 199. 



Cells single or 2-32 aggregated in fascicles, slender fusiform, acutely cus- 

 pidate at each end, straight or variously curved, 12-25 times longer than 

 broad, as much as 90 ,« long, 1.5-4 u broad. 



We may distinguish three varieties: 



Var— acicnlare (A. Br.) Rabh. Fl. Eur. Alg. III., 45. 1868. 

 Raphidinm acicnlare A. Br. 



Straight or slightly curved, attenuate at each end, 15-20 times longer than 

 diameter. PI. IV., Fig. 12. 



Var.— sigmoid in in Rabh. 1. c. 



Cells sigmoid, fusiform, single or two or four connected. PI. IV., Fig. 13. 



Var— falcatnm (Corda) Rabh. Fl. Eur. Alg. III., 45. 1838. 

 Mierasterias falcata Corda Alman. de Carlsb. 121. 1835. 



Cells fusiform, slender, curved or semi-lunar, single or 2-16 congregated in 



fascicles, 3 n broad, 6-10 times as long. PI. IV., Fig. 14. 

 In stagnant water. 



Kaphidinm conyolutum (Corda) Rabh. Fl. Eur. Alg. III., 46. 1868. 

 Acistrodesmus convolutus Corda Alman. de Carlsb. 199. 1835. 



Cells short, usually somewhat lunate, ends acuminate, green, homogeneous, 

 single or 2^ connected, usually back to back; 3.5-5 fi broad; 3-6, occasion- 

 ally even 10, times longer. 

 In standing water, Lincoln. PI. IV., Fig. 15. 



