82 DESMIDS OF THE UNITED STATES. 



ferior rounded angles to the flat, truncate end ; cytioderm 

 evenly covered with large pearly granules. Zygospores 

 orbicular, spinous with long, thin spines, the ends much 

 divided. 

 Diameter 35-62 //. 



A very common plant, and very variable in the size, and 

 in the proportions of length and breadth. 



Var. TUMIDUM, Wolle. Plate XX, tigs. 3-5. 



In outline, front view, very near C. Botrytis, yet entirely 

 unlike it in side and end views, which show a central infla- 

 tion. Found it in only one locality in a meadow pool, near 

 Bethlehem, Pa. Further observation may prove it a dis- 

 tinct species. 



C. BREBISSONII, Menegh. Plate XVI, figs. 10, 11. 



Cells somewhat longer than broad ; semi-cells semiorbicu- 

 ' lar, rough with conic spines or granules ; end view elliptic 

 or oval. 



Diameter 45-65 p. 



Cells generally larger than C. margaritij> rum ; semi-cells 

 more oval, but separable only by the armor of conical granules. 

 Not so frequent as the preceding, but appears to be widely 

 distributed. 



C. CONSPERSUM, Ralfs. Plate XVII, figs. 1, 2. 



Cells somewhat longer than broad, quadrilateral, angles 

 obtusely rounded ; constriction deep, produces a linear notch 

 on each side ; granules pearly, large, depressed, giving a. 

 crenulate appearance to the margin. 

 Diameter 50-73 //. 



A beautiful and conspicuous species, frequently found in 

 large numbers ; it is easily distinguished by its large size and 

 quadrangular form. 



C. CONSPERSUM, var. RETUSUM, Wolle. Plate XL VI, fig. 5. 



(Cornp. Des. U. S., p. 75.) 



Unlike the true form in the depressed or ret use ends ; 

 sides also incline inwardly from the base of the semi-cell to 

 the end. 



Diameter averages the same as the type-forms. 

 Ponds, Minnesota. 



C. TETROPHTHALMUM, (Kg.), Breb. Plate XVI, fig. 13. 



Cells out'-third to one-half longer than broad; semi-cells 

 semiorbicular somewhat elevated, rough with pearly granules 



