POCIDIUM. 51 



D. 8IKU0BUH, Wolle. Plate XI, figs. 6, 8 ; variety fig. 7. 



Slender, undulate, smooth, cylindrical ; 20-24 times longer 

 than broad; semi-cell with eight constrictions ; ends truncate, 

 straight or slightly concave, each angle furnished with a short 

 stout tooth ; basal inflation not plicate. 



Diameter 12-14 a. 



Var. BREVE, Wolle. (fig. 7) only half the length, and only four 

 constrictions to a semi-cell. 

 I tiameter 12-14 ;>.. 



Very oear the preceding, but armed with teeth at the apex, 

 nut plicate, and Bometimee only half the length. Pond, 

 Pleasant Mills, New Jera j . 



I >. iM.i i. \ 1 1 if, Bail. Plate X I, fig. 5. 



(Vlls small, cylindrical with undulating margins, 18-20 

 times Longer than the diameter ; moderately constricted in the 

 middle; inflation at base of serai-cells very slightly larger 

 than the undulations, apices rounded. 

 Diameter 10-12 /*. 



Bailey found thisspeciee in fresh waters of Florida ; I have 

 it from the same State, and from ponds at Hammonton and 

 Dennisville, New Jersey. 



L). hibsutum, Bail. Plate X, fig. L3. 



"Semi-cells many times longer than broad, slightly inflated 

 at base, surface hirsute, a small species resembling D.Trabecu- 

 him in form I nit strongly hirsute on its outer surface." These, 

 the word- of Prof. Bailey ; his figure has the appearance of a 

 Gonatozygon, but guided by hi- comparison with I). Trabecu- 

 lum, I judge my figure represents the same plant. The cytio- 

 derm is densely hirsute throughout. 



Diameter 24-80 n . 



Sluggish waters, eastern Pennsylvania 



D. SPINOSUM, Wolle. Plate X, fig. 12. 



( ell large, subcylindrical, 8-10 times longer than the larger 

 diameter ; margins undulate with three or four, more or less 

 prominent inflations; central constriction deep, and suture 

 conspicuous; apex truncate, about two-thirds as wide as the 



