146 MARIE V. LEBOUR. 
(20) Rhizosolenra Siolterfothii H. Perag. Perhaps the commonest of the 
Rhizosolenia species. Very common from May to September, 
with a maximum in June; disappears entirely in December. 
1500 
1400 
1300 
~ 
SN 
Soe 
| WZ 
ss 3 
re ‘ 
ao: XP 
| & < 
Oy 
SEPT. OCT. NOV. DEC. JAN. ~ FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. 
1915 1916 
Fic, 4.—Curve showing average number of Rhizosolenia Shrubsolei, Stolterfothii, 
alata, setigera, and hebetata f. semispina in 1000 ce. for each month. 
In the tow nettings it occurs in long spirals with many cells in 
each. In the water samples, however, these are broken up and 
only a few cells cling together, and many single cells are 
present. 
