24 FRESH-WATER ALG.E OF THE UNITED STATES. 



0. BREBISSONII, Delp. Plate LV, fig. 17. 



Cells sublinear, ends attenuated, moderately curved, apices 

 rounded ; about thirty times longer than broad ; cytioderm 

 smooth. 



Diameter 18 yu. 



Observed occasionally, Minnesota and Pennsylvania. 



C. LANCEOLATUM, Kg. (V. Des. U. S. p. 39). Plate LV, figs. 



18-20. 



Found hundreds of specimens of this species in a gather- 

 ing made by Prof. F. W. Cragin, Kansas. 



Diameter 40-50 /*. 



C. LUNULA, (V. Des. TJ. S. p. 40,) var. STRIATUM. Plate LV, 



fig. 12. 



Differing from the ordinary form by having the cytioderm 

 finely but distinctly striate. 



C. ACEROSUM. (V. Des. U. S. p. 41. ) Plate LXI, figs. 1, 2. 



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 dis- 

 tinctly striate. 



C. TURGIDUM. (V. Des. U. S. p. 41.) Plate LV, figs. 3, 4. 



A form differing somewhat from that figured Plate VI, 

 fig. 15. 



C. STRIOLATUM. (Comp. p. 42 Des. U. S.) Plate LV, figs. 5-8. 

 Distinct from forms heretofore illustrated, Plate VI, figs. 

 8 and 20. Fig. 8 may be considered of doubtful value. 



C. PRELONGUM, (Breb.) Delp. Plate LV, figs. 15, 16. 



Cells somewhat linear, cylindrical, elongate, about thirty 

 times longer than broad, slightly curved, apices obtusely 

 rounded, sometimes slightly recurved ; cytioderm striated. 



Diameter 20-21 j*. 



Ponds, Pennsylvania and Minnesota. 



C. SUBCOSTATUM, Nord. Plate LV, fig. 11. 



Cells usually four to five times longer than broad ; back 

 rather high arched, below nearly straight, may be either 

 slightly concave or convex ; apices obtusely rounded. Mem- 

 brane usually yellowish brown with 9-12 longitudinal costae. 



Diameter 50-60 >, 



