42 FRESH-WATER ALG^ OF THE UNITED STATES. 



Brebisson describes a French plant as St. globosum, which 

 is somewhat stouter and partially granular, but otherwise 

 nearly similar ; the two are considered forms of the same 

 species by recent specialists. 



ST. BREVISPINA, var. INERME, Wille. V. Des. IT. S. p. 122. 



A Florida form, Plate LXII, figs. 9, 10, differing slightly 

 in vertical view, but otherwise not distinct from figs. 3, 4. 

 Plate XL. 



Diameter 55-60 /*. 



ST. COSMARIOIDES, Reinsch. Plate LXII, figs. 7, 8. 



Cells large, composed in front view of two orbicular semi- 

 cells attached, forming an isthmus of one-third the diameter 

 of the cell ; margins of sides finely dentate ; in vertical view 

 triangular, angles rounded, sides slightly convex. 



Prof. Reinsch describes this form as found in Pennsyl- 

 vania, about twenty years ago. To my knowledge it has 

 not occurred since. 



ST. VESICULATUM, Wolle. Plate LIV, figs. 6, 7. 



Small, smooth, about one-half longer than broad, con- 

 striction deep, sinuses acute-angled, much ampliated ; semi- 

 cell subpyramidal, not as long as broad ; base wide, inferior 

 angles round, sides convex and inclining to a rounded apex; 

 end view triangular, angles rather broadly rounded, sides 

 slightly convex or straight. 



Diameter 31 /* ; length 45 /*. 



Differs from St. cordatum, F. Gay ; in front view, sinuses 

 are not narrow linear, but much ampliated, thereby giving 

 the cell a more elevated appearance. Green's Lake, New 

 Jersey. 



ST. PSEUDOCRENATUM, Lund. (ST. MAAMENSE, Arch.) Plate 



LVII, figs. 9, 10. 



Cells nearly one-fourth part longer than broad, suboval 

 ends somewhat truncate, deeply constricted, sinus narrow 

 linear; semi-cells subseniicircular, base straight, sides sub- 

 crenate, crenae roughly truncate-emarginate ; end obsoletely 

 erose-dentate, inferior angles subtruiicate ; in vertical view 

 triangular, sides retuse, angles broadly subtruncate, dentate 

 with three granules. 



Diameter 30-35 /i ; length 38-42 /*. 



Found this species frequent in ponds, Minnesota and Cali- 

 fornia. This form is nearest to St. crenatum, Bailey, (in 



