STAURASTRUM. 43 



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

 sinus between the semi-cells, and semi-cells are not cuneate 

 flabelliform. 



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



figs. 16, 17. 



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

 sinus acute-angled, outwardly ampliated ; semi-cells some- 

 what elliptic, back nearly straight, angles rounded, more 

 or less dentate, with large granules; in vertical view trian- 

 gular, angles broadly rounded, sides concave. 



Diameter 34-38 /. 



Green's Lake, New Jersey. 



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



Cells rather small, nearly circular, deeply constricted, 

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

 inferior angles obtusely rounded granulate-crenate. Mem- 

 brane thick, punctate, yellowish. 



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

 Tewksbury, Massachusetts. 



ST. CORNUTUM, Wolle. Plate LYII, figs. 3, 4, duplicated on 



Plate LXII, figs. 11, 12. 



Cells medium size, about one-fourth longer than broad, 

 smooth ; semi-cell oval or broadly elliptic, with a prominent, 

 somewhat inwardly curved aculeus at each angle ; end view 

 triangular, angles rounded, each with a firm aculeus, sides 

 straight or slightly concave. 



Diameter 55-60 yu; length about 70 yw, aculei not in- 

 cluded. In front view resembles a large form of Arthrodes- 

 mus convergens, but the triangular end views prove it distinct. 



Ponds, Minnesota, not infrequent. 



ST. MINNESOTENSE, Wolle. Plate LVII, figs. 7, 8. 



Cells large, punctate, spinous, about as long as broad; 

 semi-cells broadly elliptic, twice as wide as long; lateral 

 angles each with two large, straight or incurved spines or 

 aculei, three more pairs of similar spines placed within the 

 margin of the end, one of each pair on opposite sides of the" 

 semi-cell ; six more, often inconspicuous, arranged around 

 the center; end view triangular, with two spines at each 

 angle and two pairs (near the margin) between the angles, 



