26 FRESH-WATER ALG^ OF THE UNITED STATES. 



one or two undulations. Chloropkyl usually arranged in 

 numerous small parallel bands. 



Diameter 50-60 //. 



Numerous in pond, Luzerne Co., Pa. 



D. NODULOSUM, D. By. Plate LIV, fig. 3. 



Cylindrical, eight to ten times longer than broad, scarcely 

 attenuated ; undulate with three or more distinct swellings 

 in basal half of semi -cell ; apex truncate, angles rounded, 

 furnished with three or four teeth in view, below the margin ; 

 chlorophyl parietal. 



Diameter 40-50 ^. 



Pools near Minneapolis, Minn. 



D. BACULUM, var. FLORIDENSE, Wolle. Plate LIV, fig. 5. 



Differing from the typical form, Des. TJ. S. p. 49, in having 

 the margins wavy from base of semi-cell to apex. 



Diameter 15-17 ^ ; length of cell often thirty times greater. 

 Frequent in pond near Maitland, Florida, March, 1885. 



D. RECTUM, Delp. Plate LXI, figs. 20, 21. 



Cells cylindrical, straight, twelve or more times longer 

 than broad ; slightly narrower at the truncate apex than at 

 the base ; moderately swollen at the base of the semi -cells. 



Diameter 25-28 yw. 



The distinction which Delponte makes between this form 

 and D. Baculum, to which it is very closely related, is, that it 

 is perfectly straight, while the former is "straightish," some- 

 what bent, although not so represented, Plate XI, figs. 3, 4, 

 Des. U. S. The central inflations are usually larger in D. 

 Baculum than in D. rectum. 



D. WOODII, Delp. Plate LIV, fig. 4. 



Cell cylindrical, six to ten times longer than broad ; apices 

 rounded ; basal inflation of semi-cell large, wide and high ; 

 cytioderm smooth. 



Diameter at ends 50 /* ; inflation 65 yw. 

 Pond, Ocean County, New Jersey. 



D. GrEORGicuM, Lagh. Plate LXI, fig. 16. 



Cells large, twelve times longer than broad ; moderately 

 constricted in the middle; suture none; semi-cells much 

 swollen about the middle ; basal part with four larger and 

 smaller undulations, alternating large and small j ends 



