32 FRESH-WATER ALGvE OF THE UNITED STATES. 



in vertical view broadly elliptic, granulate within the margin, 

 center nude ; in lateral view suborbicnlar, end truncate. 



Diameter of cell 25 // ; length 33 //. 

 Tewksbury, Massachusetts. 



C. TAXICHONDRUM, Lund. (V. Des. U. S. p. 71.) Var. BIDEN- 



TULUM, Lagh. Plate LX, figs. 17, 18. 

 Cell sub-circular, semi-cell with one large verruca at 

 isthmus ; five large granules in an arched series between the 

 middle and the margin, and four below this in the form of 

 a cross, or a series of three and one below ; in vertical view 

 elliptic, somewhat contracted at ends, the angles bi dentate. 



Diameter 45 fj. ; length 48 ^. 

 Tewksbury, Massachusetts. 



C. PSEUDOTAXICHONDRUM, Nord. (V. Des. U. S. p. 71.) 



G. von Lagerheim appears to give too much prominence to 

 simple differ entiations mere vagaries of the same species. 

 They may be briefly noted. 



1. C. taxichondrum, var. bidentulum, as above. 



2. C. pseudotaxichondrum, cells more depressed. 



3. G. pseudotaxichondrum, var. trichondrum, semi-cells ornate 



with a single row of three granules. 



4. C. pseudotaxickondrum, var. quadridentidum ; in front 



view, the inferior angles bidenticulate. 



5. (7. pileigerum. Merely a depauperated form of the above. 

 Pond, Tewksbury, Massachusetts. 



C. QUINARIUM, Lund. Plate LX, figs. 10, 11. 



Cells subhexagonal, about one-fourth longer than broad ; 

 constriction deep linear ; semi-cells subtrapezoid, narrowed 

 toward the subtruncate apex, sides somewhat convex, inferior 

 angles obtuse, margins obsolete granulate-dentate; within 

 the margin a series of prominent granules, in center five 

 obtuse granules arranged in two transverse series ; membrane 

 punctate ; in vertical view elliptic granulate around the 

 margin j in lateral view circular. 



Diameter 33-35 /* ; length 39-42 /*. 

 Tewksbury, Massachusetts. 



C. MICROSPHINCTUM, Nord. var. PARVULA, Wille. Plate LX, 



figs. 20, 21. 



Cells small, elliptic, one-half longer than wide, moderately 

 constricted, sinus narrow linear ; semi-cell subelliptic, apex 



