STEPHANOSPHAERA. 163 



I 



Genus 36, GONIUM, Mueller. 



Coenobium composed of 4-16 cells, so arranged in a single flat 

 stratum to produce a quadrangular, tabular form, with angles 

 rounded. The whole enclosed in a colorless tegument. Cells 

 globular or by mutual pressure somewhat polygonal, bright 

 green, becoming with age disordered, granulose, connected by the 

 produced angles ; chlorophylose vesicles central, furnished with 

 colorless contractile vacuoles, and two long exserted cilia. 



Propagation by repeated division of the cytioplasm. 



GONIUM PECTORALE, Mueller. 



Coenobium flattened, quadrangular, composed of sixteen 

 green cells, furnished with vibratile cilia, usually four cells 

 in the center, and three on each side. 



Diameter of coenobia, 23-90 /*. 

 Diameter of vegetative cells, 5-15 p. 

 Stagnant waters, rare. 



The above diagnosis applies to the European plant. The 

 very few specimens found, from New Jersey and Pennsyl- 

 vania, were too limited for definite description ; they appear 

 to be the same. 



Plate CLI, fig. 15, lateral view of a coenobium ; figs. 16, 17, 

 two coenobia in front view ; fig. 18, a coenobium before 

 division. 



Genus 37, STEPHANOSPHAERA, Cohn. 



Coenobium throughout its whole life rotating and moving, com- 

 posed of eight green cells, bearing two vibratile cilia, disposed 

 at equal distances around a circle, enclosed in a common color- 

 less hyaline, globose vesicle. 



Propagation, both by macrogonidia arising from eight-fold 

 division of the green cells, bearing two cilia, with a lateral 

 red spot, congregated in families of eight ; and by microgonidia, 

 very much smaller, produced by multiplied division, at first 

 revolving within the common vesicle by the action of four cilia, 

 afterwards free, escaping singly. 



STEPHANOSPHAERA PLUVIALIS, Cohn. 



Cells globose, elliptic or fusiform, often at each extremity 

 spreading out in mucous rays. 



Diameter of coenobia, 30-60 /*. 

 Diameter of vegetative cells, 7-12 /*. 



In hollows of rocks, and in pools after rain. 



