STAURASTIfUM. 1 39 



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

 XLVIII, figs. 9, 10. 



Cells nearly one-fourth part longer than broad, suboval 

 ends somewhat truncate, deeply constricted, sinus narrow 

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

 crenate, crenae roughly truncate-emarginate; ends obsoletely 

 erose-dentate, inferior angles subtruneate; in vertical view 

 triangular, sides retuse, angles broadly subtruncate, dentate 

 with three granules. 



Diameter 30-35 //. ; length 38-42 yw. 



Found this species frequent in ponds, Minnesota and Cali- 

 fornia. This form is nearest to&'f. wenatum, Bailey, (in Ralfs' 

 Br. Des., p. 215,) but differs in having a much narrower sinus 

 between the semi-cells, and the semi-cells are not cunente 

 flabelliform. 



ST. ERASUM, Breb., var. ESPINULOSA, Lund. Plate XLVIU, 



figs. 16, 17. 



Of medium size, as long as broad, coarsely granulate, sinus 

 acute angled, outwardly ampliated ; semi-cells somewhat 

 elliptic, back nearly straight, angles rounded, more or less 

 dentate, with large granules; in vertical view triangular, 

 angles broadly rounded, sides concave. 

 Diameter 34-38 yw. 



Green's Lake, New Jersey. 



ST. LUTEOLUM, Lagh. Plate XLIX, figs. 22, 23. 



Cells rather small, nearly circular, deeply constricted, 

 sinus narrow linear; base of semi-cell straight, back arched, 

 inferior angles obtusely rounded grauulate-crenate. Mem 

 brane thick, punctate, yellowish. 



Diameter 32 //. ; length 33 /*. ; thickness 32 ft. 

 Tewksbury, Massachusetts. 



ST. COSMARIOIDES, Reinsch. Plate XLVI. 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 Pennsylvania. 

 To my knowledge it has not occurred since. 



ST. POLYMORPHISM, Breb. Plate LIU, figs. 9, 10, 24. 25. 



Semi-cells in front view broadly elliptic, with sides taper- 

 ing into short, stout processes, ends tipped with three or 

 four small spines ; membrane rough with minute, sometimes 



