130 DESMIDS OF THE UNITED STATES. 



St. elongatum, Barker. (St. terebrans, Nord.) Plate XLVI, 

 figs. 11, 12. 

 Elongate; semioells subtriangular; base globosely inflated, 

 produced into a cylindrical column inHated at the end, and 

 drawn ont 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 LI, fig. 31. 



Separated from the typical form in having in end view, four 

 rays Instead of three; in having the rays horizontal, not re- 

 flexed, and terminating with three or four strong teeth; the 

 ends of the cell- are rough with spine-like granules; the 

 base of the semioells inflated, corrugated and denticulate. 

 1 diameter 38 n.\ length 58 u. 

 IV.inl, Brown's Mills, X. J. 



St. scabrum, Breb. Plate X LI. figs. -".'. 30. 



Semioells elliptic, scabrous ; end view triangular, fringed 

 with minute emarginate spines; sides straight, angles obtuse. 

 Diameter 25-28 ft. 



Occasional in ponds, trenches and ditches, Pennsylvania 



and New Jersey. 



St. pascici loides, Wolle. Plate XLII, 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 [ cuspidate. Ends convex, angles drawn out. each into a 

 horizontal, short, -tout, tapering process, apex dentate. End 

 view triangular, sides slightly convex, angles dentate with two 

 or three acute, conical teeth. 



Diameter 27-30 >>.: length 38 n. 



Wet rocks, Lehigh Valley, Pennsylvania. 



St. ptjsillum, Wolle. Plate XLII, figs. 17-50. 



Very small, oblong, rectilinear, constriction indistinct ; 







