482 Wisconsin Academy of Sciences , Arts , and Letters. 
are made came from a collection of material near the outlet 
of Lake Monona, Wisconsin. The dimensions of the mature 
cells are within the limits given by Richter although the 
cells of the youngest colonies are smaller, measuring but 
11 y in length. 
The navicular shape of the cells, their lateral contact in 
the median part, together with a beak-like instead of a 
curved end, separates this alga from S. quadricauda (Turp.) 
de Breb. 
The number of cells in the colony is generally four, al¬ 
though two-celled colonies are not uncommon. The spines 
in this species show a great variability in both number and 
size. This again is different from S. quadricauda where their 
number and position is constant. Usually the two terminal 
cells bear a spine at each end (Fig. 181), although this is not 
always the case (Fig. 182). The presence of the spines on 
the median cells is even more variable. Not a case was 
found where every cell in the colony bore a long spine at 
each pole, although some colonies very nearly approached 
this condition (Fig. 184). The median cells have spines at 
both ends or only on one (Figs. 182, 184). Again, there is a 
great difference in the length of the individual spines, some 
being very short while others are as long as the cells (Fig. 
182). The short spines are found most frequently on the 
inner cells, although the outer cells may bear short spines 
in addition to the long spines. Richter noted this great 
variability in the presence of supplementary spines, his 
original illustrations showing conditions similar to those 
figured from my culture. 
GEOGRAPHICAL DISTRIBUTION 
EUROPE. Germany (Honigmann, 1909; Kaiser, 1908; Mars- 
son, 1904, 1911; Lemmermann, 1896, 1899, 1902, 1905B, 1905G, 
1907B, 1908D; Richter, 1896; Schmula, 1897; Schroder, 1899; 
Selk, 1905; Yolk, 1905; Zacharias, 1899, 1901). Italy (Forti, 
1905; Gugliemetti, 1910). Sweden (Borge, 1907A; Petersen, 1911). 
Switzerland (Chodat, 1901). 
AFRICA. Lake Albert Nyanza (G. S. West, 1909C). Lake 
Tanganyika (G. S. West, 1907). 
ASIA AND OCEANIA. Ceylon (West and West, 1901A) 
Java (de Wildemann, 1897C, 1899). 
AMERICAS. United States (Snow, 1903). 
