62 DESM1DS OF THE UNITED STATES. 



They may be conveniently divided as follows : 



1. Chlorophyl parietal distributed on the inside of the walls 

 of the cells. 



2. Chlorophyl more or less concentrated into one or two 

 musses, (nuclei,) in each semi-cell. 



\ Kml view round, oval or elliptic without central 

 inflation. 



1. Cytioderin (cell-wall) smooth, or punctate. 



2. Cytioderm verrucose. 



3. Cytioderm spinous.- 



', Knd view round, oval or elliptic, with a central in- 

 flation on each side. 



4. Cytioderm smooth or punctate. 



5. Cytioderm verrucose or spinous. 



C. OVALE, Kalfs. Plate XVI, figs. 8, 9. 



Large, oval or elliptical, nearly twice as long as broad, 

 ends rounded ; central constriction deep linear ; isthmus 

 about one-third of the diameter of the cell; semi-cells with 

 straight base, angles rounded and sides convex, gradually 

 converging. Cytioderm granularly rough, with one or two 

 rows of larger pearly granules near the margin, producing 

 a dentate appearance. 

 Diameter about 100 /<. (range from G2 to 112 jw.). 



Ponds, Pennsylvania, New Jersey, New York, South Caro- 

 lina, Rhode Island, Minnesota, etc. 



C. DE BARYI, Archer. (Pleurotaenium cosmarioides, De By.) 

 Plate XVIII, fig. 5. Probably the same as Calocylinrtnix 

 De BaryL Plate XLV, fig. 12. 



Cells oblong, twice as long as broad, with flatly rounded 

 ends; constriction narrow, straight, linear. Cytioderm 

 smooth or finely punctate ; chlorophyl parietal. 

 Diameter 50-54 /<. ; length 104-110 //. 



Ponds, Berkshire Mountains, Massachusetts. 



C. CUCUMIS, Cortia, Plate XVIII, figs. 6, 7, 8, 9. 



Cells oval, one aiid one-half to one and three-fourths times 

 longer than broad, ends broadly rounded; constriction linear: 

 cytioderm smooth; chlorophyl covering tin- inside of the 

 walls of the cells. 



Diameter 4(5-50 yu. Thickness 30-40 u. Isthmus about 

 one-third of the diameter of the cell. 



Frequent from Maine to Florida. 



Besides the measures given, forms are found of much 

 smaller dimensions. Figs. 7, \ ! represent such ; every pos- 

 sible size, from the largest to the smallest, and down to a 



