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IOWA ACADEMY OF SCIENCE 
139. C. moniliferum Reinsch. 
Ames. Bessey. 
Ames. Stagnant pool, by railroad. Buchanan. 
Eagle Grove. Stagnant pool by railroad. Buchanan. 
Eagle Grove. In barrel for fire protection. Buchanan. 
Eagle Grove. Slough. Buchahan. 
Eagle Grove. Jenning’s Pond. Buchanan. 
Tribe III. 
Cosmariae. 
KEY TO THE GENERA. 
Cells elongated and cylindrical; constriction slight. 
Base of semi-cells plicate 1. Docidium 
Base of semi-cells plane 2. Pleurotaenium 
Cells relatively short, commonly depressed or radiating, constriction usu- 
ally deep. 
Cells compressed (at right angles) to the plane of the front protuberance 
moderately lobed 3. Euastrum 
Cells very compressed and deeply lobed or incised 4. Micrasterias 
Cells with a more or less entire margin, often furnished with warts 
or spines. 
Cell wall smooth, granulate, verrucose, etc. Central protuberance pres- 
ent or absent 5. Cosmarium 
Cell wall with regularly arranged spines, commonly in pairs. Central 
protuberance always present 6. Xanthidium 
Cell wall without central protuberance with spines....?. Arthrodesmus 
Cells from the vertical view commonly radiating triangular, quad- 
rangular up to 11 radiate 8. Staurastrum 
1. Docidium. 
140. D. Baculum Breb. 
Ames. Pond. Buchanan. 
2. Pleurotaenium. 
141. P • trabeculae (Ehrenb.) Naeg. 
Eagle Grove. Slough amid Utricularia. Buchanan. 
Eagle Grove. Slough amid decaying rushes. Buchanan. 
3. Euastrum. 
142. E. binale (Turp.) Ralfs. 
Eagle Grove. Slough. Buchanan. 
4. Micrastorias. 
143. M. truncata (Corda) Breb. 
Eagle Grove. Slough. Buchanan. 
5. Cosmarium. 
KEY TO THE SPECIES. 
Single chloroplast (with one pyrenoid) in semi-cell. 
Semi-cell semi-orbicular C. leve 
Semi-cell subquadrate, six angled C. meneghinii concinnum 
