144 WISCONSIN PHTTOPLANKTON 



KEY TO THE GENERA. 



Cells quadrately arranged. 



Quadrate arrangement apparent in front view of cells. 



Outer face of cells without spines CBUCIGENIA 



Outer face of cells with spines TETBASTBUM 



Quadrate arrangement apparent in end view of cells TETBADESMXJS 



Cells arranged in a linear series SCENEDESMUS 



CRUCIGENIA Morren 1830. 



Coenobe free-swimming, of four cells quadrately arranged with a 

 quadrangular open space at the center and frequently connected to 

 other coenobia by a gelatinous envelope or the remains of the old mother 

 cell walls. Multiple coenobia forming a flat plate one cell in thickness 

 and containing 4, 16, 32, 64 or more cells. Cells flattened; ovoid, tri- 

 angular, trapezoidal, or semicircular in front view; with a smooth cell 

 wall. Chloroplasts l^i, parietal, disciform to laminate, with or with- 

 out pyrenoids. 



Reproduction by autocolony formation, the four cells of the coenobe 

 generally producing autocolonies at the same time. 



KEY TO THE SPECIES. 



Cells apiculate C. APIOULATUM 



Cells not apiculate. 

 Coenobe with a large rectangular open space at the center. 



Front view of cells trapezoidal C. FENESTBATA 



Front view of cells semicircular C. LAUTEBBOBNEI 



Coenobe with a small open space at the center. 

 Length of coenobe greater than the breadth. 

 Wall of cell the same thickness throughout. 



Outer face of cells concave C. CBUCIATA 



Outer face of cells convex. 



Cells of coenobe regularly arranged C. RECTANGUIABIS 



Cells of coenobe irregularly arranged C. IBBEGULABIS 



Wall of cell thicker at the poles C. TBU^CATA 



Length of coenobe the same as the breadth. 



Cells triangular, with fairly acute corners C. TETBAPEDIA 



Cells spherical to triangular, with rounded corners C. QUADBATA 



CRUCIGENIA RECTANGULARIS (Nageli) Gay. PI. 36, Fig. 3. 



Recherches sur le. dev. et la class, de quelques algues vertes 100, pi. 15, fig. 151. 

 1891. 



Coenobe four-celled, cells in mutual contact at the poles and sides 

 and with a small rectangular open space at the center. Generally 

 united in compound coenobia containing an indefinite number of coen- 



