80 
IOWA ACADEMY OF SCIENCE 
KEY TO THE SUBFAMILIES. 
Coenocytes arranged in form of a net I. Hydrodictyeae 
Coenocyte arranged in a flat plate. II. Pediastreae 
Subfamily I. 
Hydrodictyeae. 
Hydrodictyon. 
165. H. reticulatum (L.) Lagerh. 
Iowa City. Hobby. 
Forest City. Common Lime Creek. Shimek. 
Sioux City. A. E. Paddock. 
Cedar Falls. Buchanan. 
Fayette. Fink. 
Subfamily II. 
Pediastreae. 
1. Pediastrum. 
KEY TO SPECIES. 
Peripheral cells with two points P. boryanum 
Peripheral cells with four points P. ehrenbergii 
166. P. boryanum (Turp.) Menegh. 
Ames. Bessey. 
Eagle Grove. Slough, amid Utricularia. Buchanan. 
167. P. ehrenbergii A. Br. 
Eagle Grove. Slough, several collections. Buchanan. 
Family VI. 
Protococcaceae. 
KEY TO THE SUBFAMILIES. 
Cells elongated, often greatly attenuated and frequently curved. Solitary or 
loosely associated in colonies. One chloroplast per cell I. Selenastreae 
Cells globose, ellipsoid or reniform or sublunate. Daughter cells retained in 
mother cell wall, Several chloroplasts to the cell II. Oocystideae 
Cells solitary, flattened and angular, with a definite number of angles, or 
polyhedral. Angles generally furnished with simple or furcate spines 
III. Tetraedrieae 
Subfamily I. 
Selenastreae. 
KEY TO THE GENERA. 
Cells ellipsoid or much attenuated, forming more or less definite colonies con- 
sisting of a row of cells in one plane 1. Scenedesmus 
