52 SPECIES OF ALGjE. 



e. Cells, some at least, fusiform (/), 



e. Cells oblong or ovate, obtuse; 3-5 times as long as wide, 



obtusus, 173 

 /. Cells in a single even row; outer cells lunate . . dimorphus, 173' 

 /. Cells usually all alike, acute, 3-6 times as long as wide, acutus, 173 



46. SCIADIUM. 



a. Attached, umbellate; cells usually straight; base contracted into 

 a short stem arbuscula, 1 74 



a. Floating; a collection of umbels connected by a usually straight 

 cell ... gracilipes, 175 



47. OPHIOCYTIUM. 



§ One or both ends spinous (a). 



§ Without spines (c). 



a. Both ends spinous {J)). 



a. One end spinous, one end rounded; cells curved or coiled, 



cochleare, 175 



b. Cells arched or nearly straight, ends more or less enlarged, 



capitatum, 176 



b. Cells crescentic, Closterium-\ik.t, large . cuspidatum, 176 



c. Cells small, curved, often in masses, ends rounded, parvulum, 176 

 c. Cells long, narrow, repeatedly coiled, ends rounded, circinatum, 176 



48. CHARACIUM. 



§ Sessile, no stipe; cells pyriform, apex somewhat produced, 



sessile, 177 

 § Not sessile, stipe present but often short (a), 

 a. Apex rounded or truncate (b). 



a. Apex acute (d). 



b. Stipe short, scarcely noticeable, end dilated; cells producing a 



short neck acutum, 177 



b. Stipe longer, noticeable (c). 



c. Apex produced as a thick neck; stipe brownish yellow, 



Pringsheimii, 177 

 c. Apex always rounded, cells obovate, stipe base not dilated, 



Ncegelii, 178 



c. Apex rounded, truncate when open; stipe hyaline, 



heteromorphum, 178 



d. Producing a short neck; cells ovate acutum, 177 



d. No distinct neck; lanceolate or sword-shaped, ends tapering, 



ambiguuin, 177 



