52 I>h>MII>S OF THE UNITED STATES. 



D. TRUNCATUM. Breb. Plate XI. figs. 6, 7. 



Cells stout, six to eight times longer than broad, with a 

 single inflation at the base of the semi-cell, tapering to the 

 truncate, or broadly rounded, entire, ends; suture forms a 

 thick rim, which projects on each side. 

 Diameter 50-75 n. 



Florida, Minnesota, Pennsylvania. 



Peculiarities of this species are the large diameter and 

 shortness of cells in comparison with the breadth ; the at- 

 tenuated ends, truncate, or broadly rounded apices, solitary 

 inflation at the baae of the aemi-oella and consequent even 

 sides. Florida furnished the best developed forms. 



D. RECTUM, Delp. Plate X. 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 p. 



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," 

 somewhat 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. FLOTOWII ? Eab. A variety. Plate XI, fig. 5. 



Large, about eight times longer than the larger diameter ; 

 suture distinct ; solitary inflation at base of semi-cells ; sides 

 straight, tapering slightly in straight lines from the center 

 to the broad truncate apex, each angle furnished with a 

 prominent tooth ; cytioderni firm, coarsely verrucose. 

 Diameter at base of semi-cell 68 yw. ; at apex 50 /^. 



From pond on Mt. Everett, Massachusetts. A large, firm 

 and distinct form ; not identical with the described plant, but 

 it is tolerably near it. 



I). BACULUM (Breb.), D. By. Plate XIV, figs. 3, 4. 



Bather long, cylindrical, straightish margins slightly ta- 

 pering towards the ends, or nearly parallel ; apices truncate, 

 rounded. Cytioderni smooth and colorless. 

 Diameter 14-22 p. 



In general form very near D. Trabecida, but smaller and 

 devoid of the terminal vacuoles. 



Ponds, Pennsylvania, New Jersey and Florida. Bailey 

 found it also in Georgia. 



