144 DESMIDS OF THE UNITED STATES. 



drawn out into three arms somewliat refiexed at the ends ; 

 margins denticulate-undulate abore, and spinous below; 

 apices with three or four small spines. Inflated base with 

 three transverse series of small papillae; end view triangular, 

 sides concave, denticulate. 



Diameter 43^5 p.. ; length 60-75 /<. 

 Ponds, Pennsylvania. 



Var. TBTEAGONTJM, Wolle. Plate LXII, fig. 31. 



Separated from the typical form in having in end view 

 four rays instead of three ; in having the rays horizontal, 

 not reflexed, and terminating with three or four strong 

 teeth ; the ends of the cells are rough with spine-like gran- 

 ules ; the base of the semi- cells inflated, corrugated and 

 denticulate. 



Diameter 38 //. ; length 58 yU. 

 Pond, Brown's Mill, X. J. 



St. scabrum, Breb. Plate LII, figs. 29, 30. 



Semi-cells elliptic, scabrous; end view triangular, fringed 

 with minute emarginate spines ; sides straight, angles obtuse. 

 Diameter 25-2S ja. 



Occasional in ponds, trenches and ditches, Pennsylvania 

 and New Jersey. 



St. fasciculoides, Wolle. Plate LIII, figs. 54, 55. 



Small, somewhat longer than broad, granular, sheaf-form, 

 slightly constricted and notched in the middle, furnished 

 with a small protuberance on each side the notch ( front 

 view), apex 2-4 cuspidate. Ends convex, angles drawn out, 

 each into a horizontal, short, stout, tapering process, apex 

 dentate. End view triangular, sides slightly, convex, angles 

 dentate with two or three acute, conical teeth. 

 Diameter 27-30 fi. ; length 38 fi. 



Wet rocks, Lehigh Valley, Pennsylvania. 



St. pusillum, Wolle. Plate LIII, figs. 47-50. 



Very small, oblong, rectilinear, constriction indistinct ; 

 angles produced into diverging horn- like processes; end view 

 quadrangular, angles drawn out into four diverging pro- 

 cesses, ends obtuse ; membrane granular. 



Diameter 8 yu. ; length 14 /^., without the processes ; about 

 twice the measure with them. Larger form has with pro- 

 cesses a diameter of 25 /i. 



Not rare in ponds, Pennsylvania, New Jersey. 



