450 Wisconsin Academy of Sciences, Arts, and Letters. 
S. bijugatus forma arcuatus. G. S. West, 1907, p. 138. West 
and West, 1909B, p. 184. 
Coenobia 4-16 cellularum, saepe 8. Coenobis curvatis 
planis, cum parvis foraminibus inter cellulas; ceilulis in 
series duas, oblongi-ovatis vel sub-angulatis. Dimens. cell. 
9x5, 8.5x6, 12x8, 15x9 g. 
This species was isolated from a plankton catch from Lake 
Mendota, Wisconsin. For the past five years this alga has 
been found occasionally during the summer months at this 
station, but nowhere else in this locality. The measure¬ 
ments of the cells as given by Lemmermann, 7-8 y broad 
and 13-6 y long, agree very well with the dimensions of the 
mature cells both in my pure cultures, and in the field. 
The arrangement of the cells in the characteristically 
curved surface is quite striking and persits in the pure cul¬ 
ture grown in both agar and liquid media. Surface views 
(Figs. 97, 99, 100) show this well but an end view of a colony 
(Fig. 95) bring it out even more strongly. Generally the 
cells are in two symmetrically arranged series with small 
angular interstices between them (Fig. 99), but irregularities 
occasionally appear (Fig. 94). A normal colony contains 
eight cells; very few have four cells (Fig. 96), and although 
colonies of sixteen cells are reported by Lemmermann I 
have neither found them in nature, nor in my pure cultures. 
The systematic position of the form is a matter of dispute. 
It was first described by Lemmermann as a variety of S. 
bijuga (Turp.) Ktz., but later raised to specific rank. West 
and West have recently replaced it among the varieties of 
S. bijuga. This placing of S. arcuatus as a form or variety 
of S. bijuga has arisen from the conception that cells ar¬ 
ranged in two series of four cells each are a normal variation 
of *S. bijuga that may occur for one generation only. How¬ 
ever, since I have been able to isolate a form in which this 
two-seried cell arrangement persists, although the cells do 
not form a curved plane, the arrangement of the cells in 
two series may be regarded as a specific character. 
EUROPE. Austria-Hungary (Reinhardt, 1905). Germany 
(Lemmermann, 1898B, 1899, 1905B, 1907B; Marsson, 1908B, 
1911; Schmidle, 1900). Ireland (West and West, 1906B, 1909B). 
Italy (de Toni and Forti, 1899B, Gugliemetti, 1910). Sicily 
