294 
the whole roof of the hydrotheca is transførmed into the operculum 
while this within the Campanulinidae is only found in 7'etrapoma, 
Thyroscyphus (with Parascyphus) and Abietinella n. g. 
The interesting species for which I have found it necessary 
to institute the last named new genus has been described by Jåder- 
holm?) under the name of Zygophylax operculata. Like a number 
of nearly related species, referred to the genera Zygophylaæ, Peri- 
siphonia, Brucella”) and Lictorella, it possesses short-stalked, bilat- 
erally symmetrical hydrothecae, at their base provided with one or 
two nematothecae, and the colony consists of an axial tube, which 
bears at least the great plurality of the hydrothecae, and a number 
of peripheral tubes. The hydranth is provided with a blind sack, 
which no doubt is found also in the other related species, but in 
opposition to the latter the hydrothecae possess quite a similar: ad- 
cauline operculum to that found in the genera Diphasia and Åbie- 
tinaria, being at the same time of a similar form as in the latter 
genus, and especially presenting a similar neck-shaped narrowing at 
the adcauline side. In opposition to Zygophylax (Brucella) ar- 
mata Ritchie, the diaphragm of which is perforated by a large 
round opening, the diaphragm-opening of Abietinella operculata 
(pl. IV, fig. 22a) has a similar form to that found in a.number 
of Abietinaria species (pl. IV, fig. 225), being pear-shaped and 
surrounded by a projecting margin. If the proximal half of such a 
hydrotheca were to coalesce with the branch we should find in con- 
tinuation of the line, indicating the concrescence between the hydro- 
thecal wall and the corresponding wall of the branch, another line 
running downwards from the adcauline end of the diaphragma and 
indicating the corresponding concrescence between the stalk and the 
branch. Such a line, which I shall call the ,,stalk-mark”, we find 
more or less developed in all the species of Diphasia (pl. IV, 
fig. 26) and Absetinaria (pl. IV, fig. 24), and it is distinct evi- 
dence that these species must be derived from forms, which have 
1) 25, p. 276; Taf. 12 figs. 7—8. 
?) 50. 
