72 SIDNEY F. HARMER. 
pear-shaped ovicell, which replaces a zocecium at a greater or 
smaller distance from a joint, according to the species. Lichen- 
opora, on the contrary, is a plano-convex disc, usually 
closely attached by its flat surface to some foreign object ; its 
zocecia project from its upper side, and between them is a 
calcareous lamina or “crust,” which forms the roof of a large 
compound ovicell. The development of this ovicell commences 
with the early stages in the growth of the colony. Whilst a 
Crisia-colony may produce a profusion of ovicells at the 
breeding season, or may be entirely devoid of these structures, 
the ovicell of Lichenopora is a single, complicated struc- 
ture, whose growth is intimately connected with the develop- 
ment of the external features of the colony. In dealing with 
this question I am obliged to limit myself to L. verrucaria, 
the only species of which I have obtained an ample supply of 
material. It may, however, be pointed out that, if this species 
does not materially differ from other species of the same genus, 
it is the character of the ovicell which has been taken as the 
distinguishing feature of the genus or even of the family to 
which it belongs. 
According to Hincks (9, p. 471) the zocecia of the Licheno- 
poride are ‘ disposed in more or less distinct series, which 
radiate from a free central area.’’ ‘Thearea here referred to is, 
in L. verrucaria, the roof of the ovicell, and the definition 
applies only to moderately advanced colonies (Pl. 7, fig. 7), 
in which the ovicell possesses a calcareous roof. But when 
development has reached a certain stage, every colony possesses 
an ovicell, and this is in marked contrast to most of the 
Cyclostomata, in which ovicells are not present in a very large 
proportion of the colonies which may be examined. 
A still more noteworthy feature remains to be pointed out. 
The internal processes which precede the external appearance 
of the ovicell commence almost with the beginning of colonial 
life. The individual formed by the metamorphosis of the free 
larva gives rise, almost at the same time, to two new zoccia. 
One of these two commonly becomes fertile, and forms the 
starting-point of the series of stages by which the ovicell 
