144 DESMIDS OF THE UNITED STATES. 



drawn out into three arms somewhat reflexed at the ends ; 

 margins denticulate-undulate above, 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 43-45 /*. ; length 60-75 ^. 

 Ponds, Pennsylvania. 



Var. TETRAGONUM, 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 JM. 

 Pond, Brown's Mill, N. 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 25-28 /<. 



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 yu. ; length 38 /<. 



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 j*. ; length 14 /^., without the processes; about 

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

 cesses a diameter of 25 /*. 



Not rare in ponds, Pennsylvania, New Jersey. 



