22. DIDYMIA, n. gen. Table 1 figure 6.
Cells joined side by side; opening large, oval; mouth subapical, central. No avicularium. Ovicells contained within a cell, which is central at each bifurcation.
1. Didymia simplex, n. sp. Table 1 figure 6.
Cells oblong, narrowed below, broad and truncate, with an angle externally above. Back marked with transverse rugae.
Habitat: Bass Strait, 45 fathoms.
A fine species, growing in loosely-branched phytoid fronds, to a height of several inches. In some (dried) specimens the branches are a little incurved, but not in all. The situation of the ovicell is peculiar. It is contained within the upper part of a cell placed between, or rather in front of the pair, from which the two branches at a bifurcation take their origin. The ovigerous cell differs widely in form from the others, being pyriform, and much attenuated below; and the orifice is below the middle. The upper compartment, in which the ovicell or sac itself is lodged, appears to be separated from the lower by a transverse diaphragm.
23. DIMETOPIA, n. gen. Table 1 figures 7 to 9.
Cells joined back to back; the mouths of each alternate pair looking in the same direction, and at rightangles to the intermediate pair.
1. D. spicata, n. sp. Table 1 figure 9.
Cells infundibuliform. Margin of opening much thickened, with six equidistant, elongated pointed spines.