us,
which furthermore admits of being subdivided into two extremely natural
sections or subgenera (or perhaps into three). These subdivisions are
named respectively the fenestratae, and the vittatae.

In the fenestrate division, in the whole of which the cells are of larger
size and stronger than in the other, the wall of the cell appears to be
constituted of at least two distinct laminae. The external lamina, on the
front of the cell, is perforated by a certain number of holes, is wanting
rather in a certain number of spaces, for which spaces the term fenestrae
is employed. These apparent openings do not, therefore, penetrate into
the cavity of the cell. But besides the fenestrae, there is, in some
cases, a small central opening which does penetrate through the wall. In
most cases the fenestrae are arranged in a crescentic, or rather
horseshoe-shaped line, indicative, as it were, of the limits of a regular
oval space, in the front wall of the cell, the upper part of which oval
would be formed by the mouth, and the remainder filled up by the
deposition of calcareous matter, as happens for instance in the older
cells towards the bottom of the polyzoary in certain Cellulariae, etc.

A further characteristic of the fenestrate Catenicellae is the terminal
position of the ovicells. These organs are clearly transformed cells, or
cells dilated to considerably more than their natural bulk, and assuming
a subglobose form. And what is worthy of remark, these terminal ovicells
always have a sessile avicularium on the summit.

In the Vittatae the cell is smaller, and usually more delicate and
transparent. They probably want the outer lamina, or have it very thin,
and consequently present no fenestrate spaces, and the front of the cell
is beset (sometimes very sparingly) with more or less prominent, minute,
acuminate papillae. On each side, sometimes on the anterior aspect,
sometimes quite laterally, is a narrow elongated band or vitta, as it is
here designated, from which the distinctive sectional appellation is
derived. This band or stripe varies in width and proportionate length and
position in different species; it is slightly elevated, and marked with
larger, or small circular discoid, or acuminated eminences. This
subdivision is further distinguished by the situation of the ovicells,
which are not terminal, but occur at irregular intervals on cells in the
course of the series. They are of the same galeate form as in many othe