42 DESMIDS OF THE UNITED STATES. 



SECTIO^- Il.-Cells slightly bent, the back (dorsum) more or less convex, the op- 

 posite (ventral) side almost straight, distinctly attenuated from the middle to the 

 -ends. Zygospore globular, smooth. 



C. Lunula, Ehrb. Plate LXI, fig. 26. 



Cells large, semilunar, 5-6 times longer than broad, 

 smooth, or verj- finely striate, indistinct, back high convex, 

 lower side straightish, ends attenuated, rounded. Chloro- 

 phyl globules numerous ; vacuole usually distinct and con- 

 tains many actively moving granules. 



Diameter 80-110 f^. 



Frequent in small ponds. 



The figure is not a good typical form. It should not be 

 curved so much at the end. 



l^ar. STRIATUM, WoUe. (j't rj f"J '^-—^ 



Differing from the ordinary form by having the cytioderm 

 finely, but distinctly striate. 



C. CucuMis, Ehrb. Plate VII, figs. 17, 18. 



Cells smooth, stout, semiluuate ; ends broadly rounded. 

 Ehren berg's figure represents this species about five times 

 longer than broad ; in form somewhat resembling C. Lunula, 

 not so large, and lower side more concave. Ehrenberg col- 

 lected it in the State of New York. The figures are from 

 plants found in New Jersey and Pennsylvania. They are 

 evidently closely allied to C. Lunula. 



C. SUBTILE, Breb. Plate VIII, fig. 2. 



Cells very slender, acicular, slightly curved, narrow lan- 

 ceolate, apices acute, cuspidate. 

 Diameter 3-4 )x. 



Ponds, New Jersey. Rather rare. 



€. ACEEOSUM, (Schrank), Ehrb. Plate VII, figs. 7, 11. 



Linear fusiform or slightly curved, 15-24 times longer 

 than wide, lightly tapering towards the ends ; apices nar- 

 rowly truncate, or obtusely rounded, transparent or yel- 

 lowish ; cytioderm rather indistinctly, or not at all striate. 

 Chlorophyl globules 11-14 arranged in a simple axillary 

 series in each semi-cell ; vacuole small with numerous cor- 

 puscles. Zygospore globose, or broadly elliptic. 



Diameter variable, 35-62 u. 



Plate X, figs. 1, 2. A specimen finely in fruit ; presenting 

 the peculiarity of two forms of zygospores, single and twin, 

 oval, the longer axis at right angles with the axis of the 

 cells. Cell walls finely but distinctly striate. 



