62 DESMIDS OF THE UNITED STATES. 



longer, and in not having the base of the semi-cells reniform, 

 and in not having an entirely smooth membrane. Some 

 specimens are very distinctly punctate, others not so evi- 

 dently except away from the margins. Kirchner makes two 

 varieties; a. genuinum, cytioderm distinctly granular in the 

 middle ; b. subtile, cytioderm finely punctate over the whole 

 cell. 



C. 8EJUNCTUM, Wblle. Plat.' L, tig-. 18-20. 



Membrane smooth, slightly longer than broad ; semi-cells 

 semicircular with angles rounded, separated by a wide nearly 

 linear sinus; Isthmus connecting the semi-cells is narrow, less 

 than one-fourth the breadth of cells. 



Diameter 20-25 //.; Length 25-30^. 



Pond near Malaga, New Jersey, and Minneapolis, Min- 

 nesota. 



C. nitidi i.t \i, De Not. Plate Will. figs. It;, 17, 18; and 



Plate IJI, figs. '. H>. 



Cells .-mall, smooth, of nearly equal length and breadth; 

 constriction deep, sinuses narrow linear; basal angle- of semi- 

 cells obtusely rounded, Bides rounded, ends roundly truncate; 

 viewed from the vertex elliptic; from the side, subovate. 



Diameter 'I'l :;<> ;>..: length 25-35 >>.. 



Not infrequent in pond waters. The figs. li. 17, should 

 have the end- moderately Battened. 



C. P8E1 i>"M rii'i'i.i \i. Nord. Plate XVIII. fig. 19. 



Varies from the preceding in it- somewhal larger size and 

 more quadrangular form. The basal angles of the semi-cells 

 beside being rounded, protrude slightly. 



Diameter 38 fl. 



Pound this form only in Northampton County, Pennsyl- 

 vania. 



C. i.akvk, Rab. Plate XV, tig. 10. 



( 'ell- one and one-third to one and two-third- longer than 

 broad, constriction deep; -inn- narrow linear; semi-cells with 

 high-rounded end-, usually somewhat retuse Cytioderm 



finely granular. 

 Diameter 14-16 n. 



