158 DESMIDS OF THE UNITED STATES. 



rough with minute, firm, perpendicular, irregularly placed 

 aculei ; end view triradiate. 

 Spread of the arm 58-63 ^. 



Pond, Brown's Mills, New Jersey. 



The vertical spines, like the thorns of a rose, give this plant 

 a distinctive character. 



ST. QUATERNIUM, Wolle. Plate LXII1, figs. 17, 18, 19. 



Small, smooth, quadrangular in front view ; deeply con- 

 stricted ; sinus acute -angled, much ampliated ; semi -eel Is 

 oblong, sides rounded, ends truncate, each angle furnished 

 with four firm aculei; end view triangular, sides concave, 

 angles broadly rounded and furnished with four aculei, two 

 on the margin, somewhat separated, and two within the 

 margin, one on each side of the cell, and projecting between 

 the other two. By turning the cells two smaller aculei may 

 be detected near the margins of the sides. 



Diameter of body 25 /<. ; including aculei 40-50 jw. 

 Ponds, near Malaga, N. J., and Wilkes-Barre, Pa. 



ST. CORNUTUM, Wolle. Plate XL VIII, figs. 3, 4, duplicated on 



Plate XLVI, 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 //. ; length about 70 /^., aculei not included. 

 In front view resembles a large form of Arthrodesmus con- 

 rergenSj but the triangular end views prove it distinct. 

 Ponds, Minnesota ; not infrequent. 



ST. CALYXOIDES, Wolle. Plate XLVIII, figs. 14, 15. 



Nearly equal in length and breadth; smooth or finely 

 punctate; deeply constricted; semi-cells saucer- or calyx - 

 shaped, bearing on the undulate margin five equally distant 

 divergent spines ; end view pentagonal, each angle produced 

 and bearing a strong aculeus. 



Diameter about 33 //. without, and 75 jw. with, the aculei. 

 Pond, near Manchester, Ocean County, and Green's Lake, 

 Warren County, New Jersey. 



ST. FORFICULATUM, Lund. Plate LXII, figs. 16-19. 



Cells rather broader than long; deeply constricted; sinus 

 wide; semi-cells subtrapezoid, end truncately rounded ; base 



