THE GREEN ALGAE OF NORTH AMERICA 93 



upper part fits over the lower, like the cover on a pill box ; in 

 Conferva this results, when the cell breaks open, in the forma- 

 tion of the so-called H sections, formed of the upper half of one 

 cell and the lower half of the cell above it. 



KEY TO THE GENERA OF CONFERVACEAE. 



i. Cells elongate. 2. 



i. Cells globose or subglobose. 3. 



2. Cells uuited into filaments. 4. CONFERVA. 



2. Cells solitary or attached by their slender bases. 



2. OPHIOCYTIUM. 



3. Cells united into gelatinous filaments. 3. CHLOROBOTRYS. 



3. Cells solitary, free. i. BOTRYDIOPSIS. 



i. BOTRYDIOPSIS Borzi, 1894, p. 199. 



Frond unicellular, globose or subglobose, uninucleate, free ; 

 containing more or less numerous small chromatophores without 

 pyrenoid. Asexual reproduction by numerous zoospores, show- 

 ing amoeboid changes of form and having two unequal cilia. 



The type species, B. arhiza Borzi, has not been found in this 

 country, but two new species have been described, as below. 

 Nothing is known of them other than the descriptions of Miss 

 Snow, and their distinctness from the European species may be 

 questioned. 



B. ERIENSIS Snow, 1903, p. 384, PI. Ill, fig. XIII, 1-7. Cells 

 1 8-2 1 /j. diam.; chromatophores hexagonal when young, elon- 

 gate when older: zoospores usually 16 or 32 in a cell, escaping 

 through an opening in the cell wall, about 5X3 p, with red 

 stigma, and only one cilium showing distinctly. Fig. i. N. Y. 



B. OLEACEA Snow, 1903, p. 385, PI. Ill, fig. XII, i-io. 

 Similar to B . ericnsis, but less regularly globose, not over 13 //. 

 cliam., chromatophores densely packed, a red globule near the 

 center of the cell; zoospores 5-8X3-5 /* N. Y. 



2. OPHIOCYTIUM Nageli, 1849, p. 87. 



Cells free or attached to water plants, multinucleate, cylindri- 

 cal or claviform, one end frequently capitately swollen ; straight, 

 arched, curved in S-form or spirally ; solitary or in umbellate or 

 corymbose families ; at each end rounded, truncate, or mucron- 

 ate, or rounded at one end and with a stipe or spine at the 

 other; chromatophores many, parietal, without pyrenoid; cells 

 sometimes containing yellowish oil globules ; asexual reproduc- 

 tion by aplanospores, or by biciliate, ovoid-oblong zoospores, 

 formed few to many in a cell, escaping by the breaking off of 



