Blackman and Tans ley . 
190 
3 . Ancyloncma. Berggren, 1870 . 
Cell-form as in Mesotceniinn , but witli a curved parietal 
chromatophore and purple cell-sap. Cells united in 
short threads. 
4 . Penium. De Bary, 1858 . 
Cells straight, cylindrical or slightly flattened, with 
somewhat rounded ends and without equatorial 
constriction. Chromatophore consisting of radially 
diverging plates united in the central axis of the cell, 
which contains a single row of pyrenoids ; a 
vacuole often present at each end of the cell. 
5 . Pleurotanimn. Nageli, 1849 . 
Cells straight, cylindrical, slightly narrowed towards the 
ends. On each side of the shallow equatorial 
constriction a wave-like transverse swelling runs 
round the cell. Chromatophores consisting of 
several parietal bands each with several pyrenoids. 
6 . Docidium. 
Cells much as in Pleuvotcenium , the ends sometimes 
bearing branched or unbranched processes or lobes. 
Chromatophore constructed as in Penium. 
7 . Spirotania. Brebisson, 1841 . 
Cells straight or slightly bent, cylindrical with rounded 
ends, or spindle-shaped, unconstricted equatorially. 
Chromatophore of one or more parietal, spirally- 
wound bands, each with one or more pyrenoids. 
8 . Clostenuin. Nitzsch, 1817 . 
Cell semilunar or sometimes S-shaped, with tapering 
ends, symmetrical about the equatorial plane and 
one longitudinal plane only, without equatorial 
constriction, with terminal vacuoles. Chromatophore 
of radially diverging plates, united in the centre a§ in 
Penium. 
Sub-Family II. Cosmarieae. 
Cells typically oval in general outline, with a well-marked 
equatorial constriction, slightly or considerably flattened in a 
longitudinal plane. 
9 . Cosmavium. Corda, 1835 . 
Cells usually free, oval or round, with a well- 
marked equatorial constriction. Chromatophores 
two, each of four or more plates, united in the centre 
of the semicell, and containing one or two pyrenoids. 
10 . Cosmocladium. Brebisson, 1856 . 
Like Cosmavium , but cells united by pairs of 
mucilaginous threads to form branched colonies. 
