198 FRESH- WATER ALG^E OF THE UNITED STATES. 



b. Var. SIGMOIDEUM, Eab. 



Cells fusiform, somewhat sigmoid, single or two to four 

 connected. 



Syn. _R. duplex, Kg. ; R,. triplex, Eab. ; Scenedesmus duplex, Ealfs. 

 Plate CLX, figs. 24, 25. 



c. FALCATUM, (Corda. ) Eab. 



Cells slender, curved, or semi-lunar, single or four to six- 

 teen congregated in fascicles. 



Syn. Closterium falcatum, Menegh. ; Staurastrum falcatmn, Ehrb. ; 

 Micrasterias falcata, Corda.; Arihistrodesmus falcatus, 

 Ealfs, etc. 

 Plate CLX, figs. 6-10. 



d. Var. CONTORTUM, (Thur.) Wolle. 



Slender, variously curved, but mostly somewhat falcate, 

 20-30 or more times longer than the diameter. Length 

 38-50 /*. 



Collected in clusters from a few to many ; sometimes very 

 abundant, thousands of clusters in a small space in stagnant 

 waters; among them, occur not infrequently, two, three, 

 four or more long slender cells, contorted or twisted together 

 forming a body averaging 6 p by 12-15 //, which apparently 

 constitute a process of fruiting. These bodies soon break up 

 into green spherical or subspherical cells, microspores? 

 Beyond this stage have failed to trace the process. 



Syn. AnMstrodesmus contortus, Thur. 



Plate CLX, figs. 13, 14, 15, larger clusters from pool, 

 Florida; figs. 11, 12, smaller clusters preceding the twist; 

 figs. 16-21, ten forms of the contorted, or twisted, fruiting 

 specimens from Pennsylvania and Florida. 



EHAPHIDIUM BRAUNII, Naeg. 



Cells thicker than the preceding and proportionately much 

 shorter; only four to six, or rarely seven times longer than 

 the diameter, straight or moderately curved, with ends 

 attenuated ; light green. 



Diameter of cells, 5-7 ^. 

 Plate CLX, figs. 26, 27. 



EHAPHIDIUM CONVOLUTUM, (Corda.) Eab. 



The type form somewhat larger than the last (R. Braunii); 

 cells more curved; ends more acutely acuminate, green, 

 homogeneous, single or two, three or four connected, usually 



