470 Wisconsin Academy of Sciences , Arts, and Letters. 
S. quadricauda var. variabilis. Hansgirg, 1892A, p. 230. Hans¬ 
girg, 1892B, p. 119. Migula, 1907, p. 655. 
S. quadricaudatus var. setosus. Lemmermann, 1893, p. 524. 
5. quadricaudatus var. horridus. Lemmermann, 1893, p. 524. 
S. rectus. Balsamo, 1900, p. 267. 
A. qaudricauda forma Naegelii. Ghodat, 1902, p. 214; Fig. 135. 
Scenodesmus caudatus var. setosus. Conn and Webster, 1908, 
p. 35; PL VI, Fig. 34. 
Scenodesmus antennatus var. rectus. Conn and Webster, 1908 
p. 35 PI. VI, Fig. 39. 
Coenobia 2-8 cellularum, cellulis oblongo-cylindricis vel 
ovatis, utroque polo rotundatis, chlorophoris singulo, py- 
renoida singula. Apices cellularum cum singulo aculeo, 
aculeis 2-4 /x longis. Membrana cellularum sine aculeis inter 
apices. Dimens. cell. 8x4, 9x4, 11x5 /jl. 
This form is generally called S. quadricauda var. horridus , 
although Meyen was the first to maintain that spines on the 
poles of the central cells in the colony constituted a specific 
character. In his original description of the species, how¬ 
ever, this is not mentioned but the revival of the name 
longus is warranted from his statement made in 1835 where 
he compares S. quadricauda (Turp) de Breb. and S. longus 
by saying “Die Beiname quadricaudatus wiirde iibrings 
nicht passend sein, denn wir haben schon mehrmals den 
Scenedesmus longus mit ausgebildeten 16 Harnern gesehen, 
indem namlich jede Zelle 2 Harner zeigt. . 
Scenedesmus Naegelii de Breb. antedates Kirchner’s de¬ 
scription of supplementary spines on the poles of the middle 
cells in the colony. This species was founded on drawings 
by Nageli of S. caudatus Corda, one of which is seen in my 
PL XXVIII, Fig. 54. 
The varieties horridus and setosus of S. quadricauda de¬ 
scribed by Kirchner differ from one another in the number 
of spines on the poles of the median cells in the coenobe; the 
variety horridus having spines on both poles of all cells, 
whereas they do not occur on some of the mpdian cells in 
the variety setosus. 
Three different strains each having spines on both the 
middle and terminal cells as a constant character were iso¬ 
lated. This fact justifies regarding S. longus as a separate 
species. . Conversely many different strains have been 
isolated in which the spines are found on the terminal cells 
