American Paleozoic Bryozoa. 271 
.l inch, with more or less rounded apertures, that are separated from 
each other by rather thin interspaces. These, and the stellate macule, 
appear to be solid at the surface, but sections prove them to be occupied 
by a large number of small interstitial cells. 
Tangential sections (Pl. XIV., fig. 6b) clearly demonstrate the dis- 
tinctness of the species. They show that the macule are composed of 
agoreoations of very small, sub-equal, interstitial cells, the walls of 
which are comparatively thin, but never excessively so. The true 
zoccia are circular, have a diameter of about ;4,th of an inch (includ- 
ing their walls), and are in all cases more or less completely isolated by 
a row of small interstitial cells. The walls of all the cells vary slightly 
in thickness, according to the depth shown in the section. Just below 
the surface of fully matured examples, the interstitial cells are at least 
partially filled, and often much obscured by a secondary deposit. A 
rather large number of sniniform tubuli may be observed, which, how- 
ever, on account of their very small size, are al an inconspicuous 
feature in these sections. 
In longitudinal sections (Pl. XIV., fig. 6c) the tubes in the axial 
region of the zoarium are nearly eal thin-walled, and without dia- 
plragms. As they near the surface they turn abruptly outward, and 
proceed directly to the same. In the peripheral region they are more 
or less separated from each other by the small interstitial tubes, ac- 
cording as the section passes through one of the macule, or the spaces 
between them. The intervals between the diaphragms which are de- 
veloped in this portion of the true zocécial tubes, diminishes outwardly 
from about two tube diameters, to one half a tube diameter. The in- 
terstitial tubes are traversed by horizontal diaphragms, that are placed 
upon the same level in all, and excessively crowded just beneath the 
surface. An interesting fact, that may also be true of other species 
of the genus, is brought out in one of my sections: namely, all the 
small cells going to make up one of the “maculz,” are the progeny of a 
single, frequently multiplied, parent cell. 
Although this species is a true Constellaria, it differs from the 
other species and varieties of the genus, in several, more or less im- 
portant, particulars, First, in never having groups of the true zoccia 
wedged together and raised between the rays of the macula, but there, as’ 
in the intervals’ between the stellate macule, they are separated, 
more or less completely, by a series of interstitial tubes. Second, the true 
zoccia are apparently never raised above the surface, but it is the 
macule that are occasionally elevated. Third, the interstitial cells 
