32 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



division, or by the formation of four daughter-cells in a mother- 

 cell, which at length ruptures to let them out. 



Key to Genera. 



i. Cells indefinitely disposed 2 



Cells in grape-like clusters, freely exposed in a 



thin gelatinous envelope Botryococcus 



2. With well-marked. subdichotomous connecting 



threads ; chloroplast parietal Dictyosphcerinm* 



Cells in radiating series ; connecting threads scarcely 

 visible ; chloroplast axile Dictyocystis 



Description of Genera. 



Botryococcus Kiitz. Sixteen or thirty-two cells clustered 

 like a bunch of grapes in an irregularly lobed mucous thallus. 

 Cells oval, spherical, or elliptical, densely packed in families 

 within a thin tegument. Clusters free-swimming, green, at 

 length pallid or brown. 



Dictyosphaerium Nag. Cells green, kidney-shaped or 

 egg-shaped, gathered into a hollow, somewhat spherical family, 

 and usually surrounded by a gelatinous envelope; free-swim- 

 ming. Cells covered bv thick coats which are confluent; 

 joined by a fine tegument. Division of cells at first in all 

 directions, later only radially. Biciliated zoogonidia rarely 

 occur. 



D. Ehrenbcrgianum Nag., Fig. 22. 



Dictyocystis Lagerh. Oblong or cylindrical cells, held in 

 radiating series by delicate threads, to form a small, free- 

 floating colony, the series often branching. 



SUB-FAMILY II. TETRAEDRE/E. 



Solitary unicellular plants, flattened and angular with a 

 definite number of angles. The angles may be rounded, 

 notched, or furnished with spines. Only one genus, sometimes 

 divided into two, according to the depth of the lobulation. 



Tetraedron Kiitz. (Polyedrium Nag.). Cells green, 



single, free-swimming, three-, four-, or eight-angled ; angles 



pounded, sometimes notched, mostly armed with a spine. 



