THE GREEN ALGAE OF NORTH AMERICA 305 



ing, but oftener continue attached in larger or smaller numbers, 

 the families of no definite form, sometimes seeming like the be- 

 ginning of filaments ; spores of various species of algae may be 

 found germinating in company with Pleurococcus, and it is not 

 always easy to distinguish them. Miss Julia W. Snow has pro- 

 posed, 18993, p. 189, a genus Pseudo- Pleurococcus, with two 

 species, P. botryoides and P. vulgaris, but as pointed out by 

 Chodat, 1902, the characters on which the new genus is founded 

 belong also to Pleurococcus vulgaris. 



There is little or no agreement among writers on algae as to 

 what should be included in this genus other than P. vulgaris ; 

 taken in a broad sense it will include in whole or in part Proto- 

 coccus, Cystococcus, Chlorococciun , Chlorosphaera and Pseudopleuro- 

 coccus. So little is known as to American forms that might be 

 placed in these genera, that only a mention need be given of 

 such forms, with a reference that will indicate where to look for 

 fuller particulars. 



P. KiltzingiiQ. S. West, 1905, p. 287, PI. CCCCLXIV, figs. 

 9 and 10, from Barbados, is said by the author to be at once 

 distinguishable from P. vulgaris by the small size of the cells, 

 and by the yellow-green color. The diameter given, however, 

 3.8-5.7 /A, differs little from what we have noted for P. vulgaris, 

 and the shade of green in the latter varies under varying condi- 

 tions of moisture and light. 



P. regularis Artari, reported in plankton of Lake Erie, Snow, 

 1903, p. 381, PL II, fig. IX, is a problematical form, referred 

 by Chodat to Coclastruin, by Oltmanns to Ghlorclla Beyerinck, 

 itself a doubtful genus, claiming to include beside the present 

 species, the species included in this work under Palmellococcus 

 and Zooclilorclla . 



P. aquaticus Snow, 1903, p. 383, PI. Ill, fig. X, appearing in 

 laboratory cultures, must remain uncertain, as long as nothing 

 is known of it in a natural condition. 



Chlorosphaera lacustris Snow, 1903, p. 386, PL IV, fig. XIV, 

 and C. parvula Snow, I.e., p. 386, PL IV, fig. XV, must also 

 be considered questionable. 



Protococcus ovalis Hansgirg in Foslie, 1890, p. 159, PL III, 

 fig. 12. Another doubtful form; occurring in clefts of rocks 



