64 DESMIDS OF THE UNITED STATES. 



The onlj- plant I have found to harmonize with this de- 

 scription, was collected by J. D. Smith in Florida. It agrees 

 very well except in length, being nearly equal to three 

 diameters. 



<;-. PAETI-LUM. Breb. Plate XXI, figs. 12, 13. 



Cells small, ovate elliptical, slightly constricted, apices 

 truncate, two to nearly three times as long as wide ; margins 

 entire, or sometimes lightly crenulate : semi-cells short 

 conical, broadly truncate or sometimes with apex retuse : 

 cytioderm smooth or finely punctate. 

 Diameter 18-22 yu. 



Florida, collected by J. D. Smith. 



€. Ameeicaxum, Lagh. Plate XLIX, figs. 15, 16. 



Cells small, sinus rather obtuse and widening outwardly : 

 semi-cells sub-circular, the center with seven larger granules 

 (six i^eripheral and one central) and twelve, more or less 

 distinct, around these ; vertical view elliptic ; lateral view 

 sub-circirlar. Meiuljrane smooth excepting the central 

 granules. 



Diameter of cell 22 /.<. ; length 40 fx. ; thickness IS //. ; 

 diameter isthmus 6 yu. 



Pond near Tewksbury, Massachusetts. 



C. GEAXATUM. Breb. Plate LXI, fig. 13. Plate XVIII, figs. 



14, 1.5. 



Cells one and one-half times as long as broad ; constriction 



narrow linear ; semi-cells trapezoidal, with straight bases, 



rounded angles, sides gradually converging ; apex truncate : 



variable in size. 



Diameter 2o-32 jj.; i.sthmus about one-third the diameter. 



Frequent in quiet waters. Pennsylvania, New Jersey, :Mas- 

 sachusetts, Florida and Minnesota. 



Plate LXI, fig. 13, is the typical form; the others, Plate 

 XVIII, figs. 14, 15, are varieties, near Wille's variety e^ow^'a^i/zn. 



C. WoLLEANUM, Lagb., var. geaxulifeeum. Lagh. Plate 



XLIX, figs. 1. 2. Syn. C. pseudogranatum. Wolle. Des. 



U. S., p. 158. 



Cell rather large, one-fourth longer than wide ; sinus 



somewhat ampliated inwardly and outwardly ; semi-cells 



sub-semi-circular, base subreniform, dorsum narrowly 



rounded, angles rounded, margins finely crenulate-dentate ; 



