Smith—Monograph of Scenedesmus. 423 
Individual species are treated by citing the literature, 
the description (with the use of the original description as 
far as possible), a discussion of its variation as observed in 
pure culture, the geographic range. 
The first species of the genus were figured by Turpin in 
1820 as species of Achnanthes. These were illustrations only, 
but in 1828 Turpin gave a better series of illustrations and 
also described the different species. In 1829, Meyen, who 
was not aware of the work of Turpin, established the genus 
Scenedesmus and described several species. This existence 
of two sets of names has produced considerable confusion. - 
The parallelism between the species of Turpin and Meyen 
was pointed out by Guillemin in 1830, in his review of 
Meyen’s article, but no attempt was made to reduce the 
two to synonymy. 
The first combination of Turpin’s species with Meyen’s 
genus is by Kiitzing in 1833, who thought that the species 
of the two were distinct and so gave the description of both 
series. At this time Scenedesmus was placed with the Des- 
midiaceae which were thought to be a family of the Diato- 
maceae. The spelling of the name Scenedesmus is also con¬ 
fused; since Meyen spells it Scenedesmus in the text of the 
original description while on the accompanying plate it is 
spelled Scaenaedesmus. Later on he added a further varia¬ 
tion by spelling it Scaenedesmus (1830). On account of this 
vacillation in spelling and also for entymological reasons 
Ehrenberg changed the spelling to Scenodesmus. Ehrenberg 
later established the genus Arthrodesmus and transferred the 
species of Scenedesmus to this new genus. 
Between the years 1840 and 1860 various collections of 
the species of Scenedesmus are found. In these early descrip¬ 
tions the number and arrangement of the cells in the colony 
constituted the chief method by which the various species 
were distinguished, but today these characters are of minor 
importance for differentiating species. For this reason prac¬ 
tically all of the older species should be regarded as synonyms 
or placed among the questionable species. The most com¬ 
plete collections of species made at this time are those of 
Meneghini and of Kiitzing. 
The modern work on Scenedesmus really began with 
Lagerheim’s collection of the data on the known species 
