cells is connected with 6 other cells, leaving a large circular open 

 space in the center of the plate. Chloroplast a parietal cup, thickened 

 at the base, which incloses a pyrenoid; pigment-spot anterior and 

 lateral. Cells about 10/x in diameter, 1-1 1/^ times as long as wide. 



Mich. 



Gonium pectorale Mueller 1773, p. 60 

 PI. 1, Fig. 21 



Colony of (4)-8-16 ellipsoid, subspherical or sometimes ovoid 

 cells closely arranged in a flat, quadrangular plate, usually with 4 

 inner cells bordered by a series of 12 marginal ones which have their 

 anterior ends projected outward and parallel with the plane of the 

 colony, the inner cells directed at right angles to the plane. Cells 

 inclosed by individual sheaths, which are connected to neighboring 

 sheaths by very short processes. Cells 5-15//, in diameter. 



Associated with other Volvocales in hard^ water nchin_nib^ogen. 

 Mich., Wis. 



Gonium sociale (Duj.) Warming 1876, p. 82 

 PI. 1, Fig. 22 

 Colony of 4 ovoid cells, all directed outward, inclosed by colonial 

 mucilage which has a central rectangular perforation. Cells 10-15/x 

 in diameter, 12-20^^ long. 



This species, like G. pectorale, is often found in barnyard pools, 

 watering troughs, and sloughs where nitrogen content is high. 

 Eu- and tychoplanktonic; in hard water lakes. Mich., Wis. 



PANDORINA Bory 1824, p. 600 



Colony ovate or obovoid, composed of 8-16-(32) globose or pyri- 

 form cells compactly arranged and inclosed by a common gelatinous 

 envelope; cells with the broad anterior end directed outward. Chlor- 

 plast a parietal cup with 1 basal pyrenoid; pigment-spot anterior and 

 lateral. Flagella 2, arising from the anterior end of the cell and 

 diverging widely after emerging from the colonial envelope; the 

 colony swimming in a rolling or tumbling fashion; vegetative re- 

 production by the simultaneous division of each cell in the colony 

 to form as many colonies; sexual reproduction by isogametes formed 

 in groups of 8 or 16 by the partition of some or all of the cells of 

 the colony, 



Pandorina morum ( Muell. ) Boiy 1824, p. 600 

 PI. 1, Fig. 23 

 Colony usually distinctly ovate, as much as 220ju, in diameter. 

 Cells pyriform, crowded, usually 16 in number, 10-15/i, in diameter, 

 12-17/^1 long. 



[75] 



