68 DESMIDS OF THE UNITED STATES. 



C. SEJUNCTUM, Wolle. Plate LXI, figs. 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. 



Dameter 20-25 p. ; length 25-30 ^ 



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

 nesota. 



Usually two forms of this plant are recognized, the one 

 longer than the other; the longer slightly retuse, which is the 

 typical form ; the other not retuse, and not so long. 



Sometimes found in considerable numbers in gelatinous 

 gatherings on dripping rocks and in small pools. The va- 

 riety SEPTENTRIONALE, found near Amherst, Mass., not so 

 frequent. 



C. VARIOLATUM, Lund. Plate XIX, figs. 3, 4. 



Small elliptical, twice as long as wide, constriction deep, 

 narrow, linear ; semi-cells, base straight, sides rising at right 

 angles, then curving gradually and producing an almost 

 circular apex, sometimes slightly retuse ; end view broadly 

 elliptical ; side view obovate. Cytioderm more or less punc- 

 tate ; isthmus one-third of the whole diameter. Chlorophyl 

 nucleus single. 

 Diameter 15-17 /<. 



Ponds, southern New Jersey, Hammonton, etc. 



C. CIRCULARE, Eeinsch. Plate XLVIII, fig. 37. 



Cells nearly circular ; present form slightly shorter than 

 broad ; sinuses narrow linear ; lateral view ovoid, end view 

 elliptic ; isthmus one-third of diameter of cell ; membrane 

 finely punctate. 



Diameter 75-85 /*. ; length 70-75 p. 



Frequent in marsh pools, Tocoi, Florida. This form is con- 

 siderably larger than the one described by Reinsch, and not 

 quite equal in length and breadth, but otherwise very near it, 

 and certainly nearer than the plant described by Lundell 

 under the same name. 



C. CONTRACTUM, Kirch. Plate XIX, fig. 1. Plate LXI, fig. 24. 

 Cells one and one- half times as long as wide ; sinus pro- 

 duced by the constriction, deep and narrow, widening out- 

 wardly from the base. Semi-cells oval, with convex base 



