Contributions to Our Knowledge of the Freshwater Algae of Africa. 29 
1. Cosmarium pachydermum, Lunde]l, Desm. Suec, 1871, p. 39, Tab. II, 
fig. 15 ; W. & G. S. West, o]j. cit., II, 1905, p. 139, PI. LVII, fig. 7. 
var. tuberculatum, F. E. Fritsch, nov. var. (Fig. 10). 
Cellulis ca. Ifplo longioribus quam latis, a latere visis lateribus minus 
convexis apicibus minus rotundatis et cum membrana incrassata ; semi- 
cellulis cum tuberculo late rotundato infra apicem utrobique e excavatione 
vadosa orto. 
Long, cell., 70-90 ; lat. cell., 48-58 /x ; lat. isthm., 18-26 /x ; crass., 
30-36 /i. 
Sample 327 (very rare). 
This variety differs from the type in three respects, viz. the relation 
between length and breadth of the cell (the semicells being more circular 
than elliptical), the shape of the semicells in side-view, and the broad, 
rounded tubercle occurring a little way beneath the apex in the median 
line of each semicell (Fig. 10, A). This tubercle arises from the base of 
a shallow depression, — a fact which is particularly obvious in the end-view 
(Fig. 10, 0) ; in the front-view it only becomes distinctly visible on 
focussing down to about one-quarter of the thickness of the semicell. This 
variety, in the possession of this feature, appears to bear much the same 
relation to C. jjachydermum, Lund., that C. aitchisonii, Schaarschmidt 
(" Afghanistan Algae," ' Journ. Linn. Soc, Bot.,' xxi, 1884-5, p. 246, PI. V, 
fig. 20) does to C. nitidulmn, De Not. The end- and side-views of 
0. aitchisonii, Schaarschmidt, are, however, not known, but should they 
Genus COSMAEIUM Corda. 
