36 University of California Publications in Botany [Vol. 6 



The coenobinm (pi. 7, fig. 1) is subcircular in axial view, elliptical 

 in lateral view, and lenticular in general form, but modified in detail 

 by the exposed surfaces of the constituent cells. Its major axis is 

 short, the axial diameter of the coenobium being about one-half that 

 in the minor axes. It is made up, in the individual figured, of sixteen 

 subequal cells with a very characteristic arrangement. At either pole 

 is a group of four cells and in the periphery of the lenticular mass 

 are arranged the other eight cells in four groups of two each. The 

 circular outline is thus somewhat modified toward the quadrangular 

 by this grouping of the marginal row of cells. The coenobium is solid, 

 without central cavity, since the two polar quartets abut one upon 

 the other in the equatorial plane about the main axis. They thus form 

 a sort of axial parallelopipedon with rounded ends and corners and 

 constricted equatorial region where the inner ends of the two quartets 

 meet. Into this equatorial depression the outer circle of eight cells 

 fits as an automobile tire into the rim of the wheel. The cells of 

 each apical quartet form a quadrangular group, each almost exactly 

 superposed upon the other, with an axial depression at the pole, 

 rounded angles, and a slight notch at each furrow as seen in axial 

 view. Thus the two furrows which separate the cells of one of the 

 quartets are directly continuous with those of the other, and also 

 coincide with two of those parting the cells at the j^eripheral ring. 

 These two main planes thus divide the coenobium completely into 

 quadrants and lie in the two minor axes. 



The two apical quartets are similar in all respects, except that 

 the apical depression at one pole (fig. 1) is not so large as at the 

 other (fig. 2) and the line of apposition of two diagonally opposite 

 cells which stand at a slightly higher level than the other diagonally 

 opposing pair, is less pronounced. The opposite pole (fig. 2) is also 

 .'cr.^f.vhat flatter, but this may be mere individual variation and have 

 no significance suggestive of a sessile habit or attachment at some 

 phase of the life-history, or of some relation to other coenobia in 

 development. 



A consideration of the the arrangement of the individual cells in 

 the coenobium (pi. 7, figs. 1-3) at once suggests certain similarities to 

 a morula stage of an animal egg, in which equal cleavage of the 

 radial type has progressed through the fourth division, resulting in 

 sixteen cells of the fourth generation. The arrangement of cells here 

 described could be derived from an eight-cell stage with radial super- 

 posed quartets by division and shifting of the proximal (equatorial) 



