So A 
aay, lua 
260 Cincinnati Society of Natural History. 
interstitial spaces are always wider than on the concave portions of 
the surface. 
Good and satisfactory tangential sections of. this species are diffi- 
cult to prepare, on account of the extreme brevity of the fully matured 
portion of the zoarium in most specimens. One of my sections gives — 
a fair idea of the characters of the peripheral portion of the zoarium, 
and shows (Pl. XIIL, fig. 2a) that just below the surface of matured 
specimens the true cells are approximately oval, and marked by rather 
thick, ring-like walls, within the substance of which one or two rather 
large spiniform tubuli are developed ; they are sometimes in contact, 
but usually separated by large, somewhat unequal and angular inter- 
stitial cells, having much thinner walls. In a few spots the minutely 
perforated pellicular covering of the latter is shown. When the sec. 
tion passes through a slightly deeper level, the two sets of cells are 
scarcely distinguishable, both being now polygonal, with thin walls, 
frequently a little thickened at the angles of junction, and at irregular 
intervals more strongly so, wken occupied by a spiniform tubulum. 
The lower and left hand sides of figure 2a, represents a part of the sec- 
tion in which the cells are just passing from this stage into the more 
matured phase before described. 
Longitudinal sections (Pl. XIII, fig. 2b) show that the tubes in the 
axial region are comparatively large, excessively, thin-walled, without 
diaphragms, and that they proceed in their course from their point of 
origin to the surface, with but a slight degree of curvature, that at no 
point is abrupt. When near the surface their diameter is somewhat 
lessened by the development of the more or less rapidly expanding in- 
terstitial tubes. The latter present a beaded appearance, being con- 
stricted at diminishing intervals, each being marked by a complete 
horizontal diaphragm. In the true tubes diaphragms are often want- 
ing throughout, and in no case have I ever detected more than two in 
any one tube, these being placed, in all cases, one near the aperture, 
and the other near the origin of the interstitial tubes. The section il- 
lustrated represents a more matured state than is usual, and in the 
majority of sections, the outer dense portion will not be observed. This 
dense terminal portion of the zoarium may consist of only a single 
layer, or of several more or less obscurely defined layers, each of which 
is perforated by mirute foramina, and properly belongs only to the in- 
terstitial tubes, as they represent periodic reproductions of the pellicu- 
lar interstitial covering. In this, the fully matured stage of the zoari- 
um, also the walls of the proper zocecia, when a side is laid bare, are 
apparently perforated by similar foramina. 
