IOWA ACADEMY OF SCIENCE 
77 
Two chloroplasts (with two pyrenoids) in each semi-cell. 
Membrane smooth or lightly punctate. 
Nine crenae to semi-cell C. undulatum 
Ten-fourteen crenae to semi-cell C. undulatum crenulatum 
Membrane verrucose, rarely heavy punctate. 
End of semi-cells broadly rounded C. margaritiferum 
End of semi-cells truncate. 
Diameter 35-62 u.. C. botrytis 
Diameter 25-30 u C. notabile 
11*1*. C. leve Rabenh. 
Fayette. Fink. 
11*5. C. meneghinii var. concinnum Rabenh. 
Eagle Grove. Slough. Buchanan. 
11*6. C. undulatum Corda. 
North Gar Lake. Buchanan. 
11*7. C. undulatum var. crenulatum. 
Eagle Grove. Slough. Buchanan. 
11*8. C. margaritiferum Menegh. 
Ames. Bessey. 
11*9. ' C. botrytis Menegh. 
Iowa City. Hobby. 
150. C. notabile Hansg. 
Eagle Grove. Slough, amid Utricularia. Buchanan. 
Eagle Grove. Slough, decaying rushes. Buchanan. 
6. Xanthidium. 
151. X. antilopaeum Kuetz. 
Eagle Grove. Slough. Buchanan. 
7. Arthrodesmus. 
152. A. Incus (Breb.) Hass. 
Eagle Grove. Slough. Buchanan. 
8. Staurastrum. 
KEY TO SPECIES. 
Very small, diameter 16-25 u S. pygmaeum 
Larger. 
End view circular $. margaritaceum 
End view triangular 5. polymorphum 
End view 4-6 angled S. crenulatum 
153. S. pygmaeum Breb. 
Eagle Grove. Slough amid Urticularia. Buchanan. 
151*. 8. margaritaceum Menegh. 
Eagle Grove. Slough. Buchanan. 
155. S. polymorphum Breb. 
Eagle Grove. Slough amid Utricularia. Buchanan. 
Eagle Grove. Slough amid decaying rushes. Buchanan. 
156. S. crenulatum (Delp) Naeg. 
Eagle Grove. Slough amid Urticularia. Buchanan. 
