120 DES.MII>- OF THE UNITED STATES. 



St. orbktlare, (Ehrb.) Ralfs. Plate XXXIX. figs. 9, 10. 



Orbicular, constriction narrow linear: semicells not elliptic, 

 but semiorbicular ; end view triangular, angles rounded, sides 

 somewhat concave ; smooth. 

 Diameter 30-45 u. 



Variable in size, and appearance sometimes the sides are 

 more concave than figured and the sinuses between the semi- 

 cells are not always so closely linear. It is a common species. 



St. tumidi m, nreb. Plate XXXIX, figs. 1, 2. 



Large, Bomewhat Longer than broad, deeply constricted, with 

 a distinct colorless gelatinous covering; semicells elliptic or 

 suborbicular ; end view bluntly triangular, sides somewhat 

 convex, -lightly constricted near the angles, producing a 

 nipple-like projection. Margins appear striated. 

 Diameter 1 12 ft. 



The only habitats hitherto discovered, are marsh pools, 

 Bucks County, Pa. 



St. grande, Bulnh. Plate XXXIX, figs. ">, 4. 



Large, length and breadth the same, Binuses acute, much 

 enlarged outwardly ; semicells elliptic, angles obtuse ; end view- 

 triangular, rarely quadrangular, sides -lightly retuse, angles 

 obtuse; membrane finely punctate. 

 Diameter 75-83 ft. 



Marsh pools, Minneapolis, Minn. 



The specimens wen- some time in a weak solution of car- 

 bolic acid before being examined, and in consequence the 

 arrangement of the chlorophyl was destroyed; omitting this 

 consideration they agree well with measures and form de- 

 manded by the diagnosis of the author. 



St. magnum, Wolle. Plate XXXIX. figs. 7,8. 



Cells nearly one-third longer than broad; sinuses sub- 

 rectangular; semicells broad elliptic with a short, stout, erect 

 mucro at each end ; end view triangular, sides straight or 

 slightly concave, angles mucronate. 

 Diameter 82 //. ; length 100 ,". 



This species, like St. tumidum, is usually surrounded by a 

 wide, colorless, gelatinous sheath. I have this species from 

 Florida, collected by J. D. Smith. 



It is separated from the preceding by its intermediate size, 

 proportionately greater length and the mucronate angles. 



