56 PE^IIIDS OF THE UXITED STATES. 



the middle : inflation at base of semi-cells very slightly 

 larger than the undulations, apices rounded. 

 Diameter 10-12 /.i. 



Bailey found this species in fresh waters of Florida ; I have 

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

 Dennisville, New Jersey. 



D. HiESUTUM, Bail. Plate XIII. fig. 13. 



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

 flated at base, surface hirsute, a small species resembling D. 

 Trabecula in form, but strongly hirsute on its outer surface." 

 These, the -n-ords of Prof. Bailey : his figure has the appear- 

 ance of a Gonatozygon, but guided by his comparison with 

 D. Trabecula, I judge my figure represents the same plant. 

 The cytioderui is densely hirsute throughout. 

 Diameter 24-30 yu. 



Sluggish waters, eastern Pennsylvania. 



D. spiNosuM. ^'olle. Plate XJII, fig. 12. 



Cells 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 conspiciious ; apex trtmcate. about two-thirds as wide 

 as the base of the semi-cell, cytioderm firm, clothed with 

 densely set spines ; two or three rows around the apex firmer 

 and longer than the others. 

 Diameter 40-4.S /<. 



Pond, Dennisville, New Jersey. 



D. crenalatum, Ehrb., D. nodosum, Bail.. D. hirisutum, Bail., 

 have features in common with this form. I have separated 

 it in view of the armor of spines with which it is clothed ; 

 these are not hairs, nor gelatinous contractions, but decided 

 and firm spines. 



D. VEREUCOSUM, (Bailey ). Ralfs. Plate XIII, figs. 4, 5. 



Cells cylindrical, tapering very slightly from the center to 

 the apex ; margins made erenate by niimerons whorls of 

 quadrangular prominences. Length about twelve times the 

 breadth. 



Diameter 2.5-33 u. 



Occurs frequently in ponds, Mt. Everett, Mass., and sparsely 

 in quiet waters, northern Xew Jersey. Bailey found it oria- 

 inally in Rhode Island and New York. 



