64 WISCONSIN PHYTOPLANETON 



Cell wall with granules. 



Lateral angles rounded (6) S. alternans 



Lateral angles acute or truncate. 



Vertical view with angles truncate (7) S. denticulatum 



Vertical view with angles acute. 



Angles with a single curved spine (9) S. lunatum 



Angles with two divergent spines (8) S. avicula 



(B) Cells with long spines at angles or on cell body. 

 Spines confined to angles. 

 Vertical view triangular. 

 Isthmus elongate. 



Apex of semicells concave. 



Vertical view with sides indented (10) S. aristiferum 



Vertical view with sides not indented (11) S. curvatum 



Apex of semicells convex. 



Spines short and upwardly divergent (12) S. dejectum 



Spines long and subparallel (13) S. cuspidatum 



Isthmus not elongate. 



Semicells transversely elliptic (15) S. Dichiei 



Semicells obversely triangular. 



Cells small and angles submamillate (16) S. connatum 



Cells large and angles acute (14) S. megacanthum 



Vertical view quadrangular. 



Angles with a single spine (10) S. aristiferum 



Angles with more than one curved spine (17) S. quadrangulare 



Spines on angles and on body of semicells. 



Spines all the same size (18) S. hreviaculeatum 



Spines of two sizes. 



Median portion of cell apex without spines. 



Semicells elliptic (20) S. minnesotense 



Semicells hexagonal (21) S. spiculiferum 



Median portion of cell apex with spines (19) S. setigerum 



(A) Angles of cells continued in hollow processes. 

 (C) Processes in one whorl. 



(D) Vertical view triangular. 



Processes smooth (22) S. hrachiatum 



Processes variously ornamented. 

 Apex of semicells without verrucae. 



Ends of processes with long divergent teeth (23) S. pseudopelagicum 



Ends of processes with short teeth. 



Semicell bases with a transverse ring of granules (24) S. cingulum 



Semicell bases without transverse ring (25) S. paradoxum 



Apex of semicells with verrucae. 

 Two verrucae on each side of cell. 



Processes short (26) S. protectum 



Processes long. 



Ends with two long divergent spines (34) S. lacustre 



Ends with short divergent teeth. 



Processes subparallel (29) S. floriferum 



Processes upwardly curved (30) S. Bullardii 



More than two verrucae on each side of the cell. 



