156 DESMIDS OF THE UNITED STATI> 



Found this form frequent in material collected in small 

 pools near Lake Tahoe, California, by Mr*. Hanson and Miss 

 Haggin, of San Francisco. 



ST. MINNESOTENSE, Wolle. Plate XLVIII, figs. 7, s. 



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, 

 on each side of the triangle; around the center are nine 

 more spines, often indistinct. 



Diameter (>5-75 v. without, and 90-100 //. with the spines. 

 Frequent in Minnesota ponds. 



ST. TRIDENTIFERUM, Wolle. Plate LVI, figs. 9, 10. 



Very small, smooth, sinus ample ; semi-cells elliptic, ends 

 more or less convex, angles furnished with three, firm. <li 

 verging aculei ; end view triangular, sides retuse, angles 

 with three large aculei. 



Diameter 17-20 /^., without spines; with them 25-28 jw. 

 Sluggish waters, Pennsylvania. 



ST. CRUCIATUM, Wolle. Plate LVI, figs. 11-13. 



Small, smooth, front view cruciform, lobes short linear, 

 ends rounded ; sinuses wide, rectangular ; end view three or 

 four lobed, slightly tapering, ends rounded and furnished 

 with a number of more or less diverging setae, which are 

 as long as the lobes. 



Diameter 25 /*., without setae. 

 Ponds, Northampton Co., Pa. 



ST. CERBERUS, Bailey. Plate LVI, figs. 7, 8. 



"Cells small, deeply constricted, semi-cells three lobed; 

 lobes with four teeth, two of which project upwards and two 

 downwards, at each truncate angle." 

 Diameter 25-30 yu. 



This species is reported by Bailey, from lakes in Florida. 



ST. HYSTRIX, Ealfs. Plate LVI, figs. 14-16. 



Semi-cells in front view subquadrate, extremities some- 

 what rounded, end margins nearly straight, furnished with 



