274 Carter . — Studies on the Chloroplasts of Desmids. III. 
semi-cell which is somewhat similar in form to those of C. punctulatum , 
C. depression , &c., but differs from these in the arrangement of the pyrenoids. 
As in the simple chloroplasts of these small species, there is a central axis 
containing usually one pyrenoid (Text-fig. i, c), but this may occasionally 
bud off others. From this axis four lobes are given off, which expand to 
form somewhat massive parietal plates, two of which lie against each front 
face of the semi-cell (Text-fig. i, c). Commonly there is a large pyrenoid 
in each of these lobes, equal in size to the central pyrenoid, so that the 
typical number of pyrenoids is five (Text-fig. 1, d). Those in the lateral 
lobes of the chloroplast, however, are not so constant as the central one, and 
occasionally one or more of the lobes may be entirely free from them, whilst 
in others, if present, the pyrenoids are very reduced in size, and look as if 
they had been formed de novo. In one semi-cell at least eight such tiny 
pyrenoids were observed in these lateral lobes (Text-fig. i, E). The most 
common type, however, had a large pyrenoid in each of the four lobes in 
addition to the central one, and in every individual examined at least one 
semi-cell showed this structure. 
C. psendoconnatum. 
The chloroplast of this species is rather different from that of any other 
species examined. It was originally believed to have parietal chloroplasts, 
but is mentioned by Lutkemiiller (1893) as being the only species included 
in Pleurotaeniopsis in spite of the fact that it has an axile chloroplast, 
because it was known to have four pyrenoids in each semi-cell, whilst in 
Cosmarium proper there were only supposed to be one or two. . 
The chloroplast of C. psendoconnatum consists of four large wedge- 
shaped masses arranged symmetrically in each semi-cell, each mass con- 
taining typically one pyrenoid, and all four being united in the interior by 
their thin ends (Fig. 36). Towards the periphery the broad external surface 
of each mass is grooved to form irregular ridges, whose edges spread out 
over the cell-wall (Fig. 35). 
C. ornatum and C. Ralfsii. 
C. ornatum and C. Ralfsii have chloroplasts which show some similari- 
ties whilst being different from those of any other species examined. The 
smaller species, C. ornatum , has an axile chloroplast in each semi-cell, con- 
sisting of a relatively short broad axis, containing two or three pyrenoids, 
with about eight plates radiating in various directions towards the periphery 
(Figs- 33 and 34)- 
The larger species, C. Ralfsii, was for a long time supposed to have 
parietal chloroplasts, and was placed by Lundell (1871) in his sub-genus 
Pleurotaeniopsis, together with other species having parietal chloroplasts. 
Lutkemiiller (1910) corrected this mistaken idea by means of a short note 
and figure. The chloroplast in this species consists of a broad axis occupying 
