40 West & West. — Observations on the Conjugatae. 
Sub-fam. 2. — Pyxisporeae . 
This family is represented solely by the genus Pyxispora 
obtained from West Central Africa 1 . The vegetative cells, 
which are about 12-13*5 m in thickness, contain two chroma- 
tophores very similar to those present in Zygnema , and in 
the sterile condition the plant could not be distinguished 
from the vegetative filaments of a species of the latter genus ; 
each of these chromatophores has a small central pyrenoid. 
The conjugation is scalariform and similar to that present in 
the Mesocarpeae, resulting in an immediate tripartition into 
a sporocarp consisting of two sterile cells and an intervening 
carpospore. 
The characters of this carpospore are unique, and sharply 
demarcate this genus from any other in the Zygnemaceae. 
It is broadly elliptical with rounded poles : it is disposed 
transversely to the longitudinal axes of the conjugating 
filaments, and around its edge, in the plane of its shorter 
diameter, is a small annular ridge marked by a circumscissile 
crack. 
Some further figures of this interesting genus are given 
(Figs. 53 and 54). 
Sub-fam. 3. — Zygnemeae. 
This is the largest family of filamentous Conjugatae, and 
includes the five genera, Zygnema , Pleurodiscus , Spirogyra, 
Sirogonium , and Debarya. 
The chromatophores of the genus Spirogyra , according to 
some botanical text-books, ‘take the form of green spiral 
bands with toothed edges ’ ; this is often true, but throughout 
the genus they exhibit much variation, there being every 
gradation between the slender, perfectly smooth spirals of 
S. neglecta with their axile uniform series of pyrenoids, and 
the broad serrated spirals of S', nitida and S. porticalis , 
containing scattered pyrenoids of various sizes. In fact, the 
1 West and G. S. West, Welw. Afric. Algae, Journ. Bot. 1897, p. 39. 
