ZOOPHYTOLOGY. 158 
6. Fam. GremeLnartap#, Busk. 
1. Didymia, Busk. 
1. D. simplex, Busk. 
2. Dimetopia, Busk. 
]. D. spicata, Busk. 
2. D. cornuta, Busk. 
3. Calwellia, n. g. 
Cells in pairs, joined back to back. ach pair of cells arising by tubular 
prolongations from the pair next but one below it. ach pair having a 
direction at right angles to the next. At a bifurcation each cell of the 
primary pair giving off a secondary pair. Ovicell subglobular, placed im- 
mediately above and behind the posterior margin of the cell-aperture. 
l. C. bicornis, n. sp. 
The only known species. 
This genus supplies another link in the beautiful chain of 
modifications in the arrangement of cells in pairs furnished 
by the Gemellariade. By combining one of the peculiar 
characters of Notamia with a genera, appearance closely re- 
sembling Dimetopia, it affords another reason for retaining 
Notamia in the group, bearing, in fact, with the exception of 
the total absence of avicularia, the same structural relation 
to Notamia which Dimetopia bears to Gemellaria. The 
lower half of each pair is contracted and tube-like, the two 
lobes of which it is composed separating and curving over 
the walls of the inflated triangular upper half of the pair im- 
mediately beneath it. The coencecium is thus formed of 
two incorporated, independent rows of pairs of cells, all the 
cells of each row being in the same plane, but at right 
angles to all the cells of the other row. This somewhat 
complicated structure might be better understood, as the 
author states, if the reader would imagine another exactly 
similar double-stem incorporated at right angles with fig. 2a, 
Plate IX of the original memoir. 
The cell-mouth is small, nearly horizontal on the upper 
surface of the cell. The margin is thickened, rising at the 
outer angles of the nearly straight lower lip into a pair of 
strong, incurved, blunt spines. The cell-wall seems to con- 
sist of two membranes, and round the lower lip and at the 
base of the spines there are a few small, oval and round, 
fenestre, passing apparently through one layer only. <A 
small, granular, perforated papilla rises immediately below 
the cell-mouth, the oval aperture passing right through the 
cell-wall. 
The ovicell is immediately above and behind the m oh of 
the cell, cemented against the triangular side of the pair of 
