62 DESMIDS 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 

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



g End view round, oval or elliptic without central 

 inflation. 



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



2. Cytioderm verrucose. 



3. Cytioderm spinous. 



§ End 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, Ealfs. Plate XVI, figs. 8, 9. 



Large, oral 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 62 to 112 /./.). 



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

 lina, Rhode Island, Minnesota, etc. 



C. De Baeyi, Archer. (Pleurotaenium cosmarioides, De By.) 

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

 De Baryi. 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, Corua. Plate XVIII, figs. 6, 7, S, 9. 



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

 longer than broad, ends broadly rounded; constriction linear; 

 cytioderm smooth ; chlorophyl covering the inside of the 

 walls of the cells. 



Diameter 46-56 /'. Thickness 36-40 li. Isthmus about 

 one-third of the diameter of th'b cell. 

 Frequent from Maine to Florida. 



Besides the measures given, forms are found of much 

 smaller dimensions. Figs. 7, 8, 9 represent such ; every pos- 

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



