104 
as he did not include any of them in his List. Desm. 
Norm. 1856, although these algæ were first gathered 
in Normandy and yet he there described an allied small 
species, Spir, minuta Thur, in litt. 
The first description of Docidium Bréb. in Diet, 
univ. hist. nat. vol. 5, 1844, runs thus ”- pour¬ 
vus d’un endochrome non lamelleux ni rayonnant, 
mais forme de bandelettes anastomosés tapissant in¬ 
térieurement la carapace d’une sort de réseau- 
remplis d’un endochrome en lanières anastomosées 
— — — par la disposition anastomosée de l’endo- 
chrome qui n’est point en lamelles rayonnantes. Le 
Docidium Ehrenbergii Bréb., et D. haculum Bréb. 
sont figurés par M. Ehrenberg, dans son grand ou¬ 
vrage sur ' les Infusoires, pl. 6 f. 2 sous le nom de 
Closterium traheeuW. His third, not named species 
was, I suppose, D. truncatum. 
Nä geli in 1849 elevated Closterium Trabecula 
Ehrenb. to generic rank under the name of Pleuro- 
tsenium for the same reason as Brébisson: ”— in 
jeder Hälfte mehrere grüne Längsbänder, welche an 
der Wandung liegen, in jeder Bande eine Reihe von 
Chlorophyllbläschen” (Gatt. einz. Alg. p. 104). When 
Nägeli in June 1848 dated the preface of his work, 
he surely had not seen Ralfs’ Brit. Desm., and pro¬ 
bably not Diet. hist. nat. 5. Thus both authors foun¬ 
ded their genera on the same data, the structure of 
the chloroplasts. However, these two genera have 
in later time been accepted upon other characters, 
given by Lund ell 1871 in Desm. Suec. According 
to him Fleurotcenium has parietal chloroplasts with an 
apical vacuole, but without basal plications, and Doci¬ 
dium has one axile chloroplast without any apical 
vacuole, but with basal plications. Lunde 11 quotes 
under his Doc. Baculum Ralfs Brit. Desm., but he 
quotes Bréb. Alg. Fal. only with a ?, because the 
entire absence of plications at the base of the semi- 
