= “ee ee ee 
278 Cincinnati Society of Natural History. 
portion of the zocecia, and are crossed by a few diaphragms, Apertures 
of trne zocecia closed by opercula. 
This genus differs from all other bryozoa known to me, by its com- 
plicated system of inter-communication. 
HELIOTRYPA BIFOLIA, n. sp. (PI. XIIL, figs. 6-6e.) 
Zoarium consisting of two thin leaves, grown together back to back, 
by the adhesion of their basal membranes. Each has a thickness of 
about 54th of an inch, and the largest expansion noticed, has a super- 
ficial area of about three square inches. True zoccia very regularly 
arranged in quincunx, or in longitudinal and transverse series, with 
moderate vestibules, and circular apertures. At intervals of .1 inch, 
measuring from center to center, the surface exhibits small “ maculz,” 
around which the true zoecia are a little larger than in the intervening 
spaces. ‘Ten or eleven of the ordinary size occupy the space of .1 inch. 
The actual orifices are separated from each other by interspaces twice 
as wide as their diameter, and, on protected spots, preserve the cen- 
trally perforated opercular covering. The interstitial tubes are repre- 
sented by numerous small pits in the * macule’ and interspaces 
between the vestibules of the true zowcia. They are often more numer- 
ous than is shown in figure 6. Besides these, the mouths of a vast 
number of minute pores may be observed in the substance of the walls. 
Tangential sections (Pl. XIIL., fig. 6a) show that the true zoecia are 
more or less in contact, the line of contact being marked by a closely 
arranged series of vertical tubuli, which also define, but less distinctly, 
the outlines of the thick-walled interstitial ceils. The true zocecia 
have an average diameter of about zi;th of an inch, while that of the 
visceral cavity is about 54,th inch. If the section is not too thin, and 
cuts the zoarium just below the surface, a large number of minute 
tubuli are shown to pass through the walls of the SE ina radial 
manner around their visceral cavities. 
Longitudinal sections (Pl. XIII., figs. 66 and 6c) show that the 
zoarium consists of two separate leaves, the basal membranes of which 
adhere to each other. Between these, as well as between the double 
cell-walls in the “immature” or inner region of the zoarium, there may 
be detected a large number of minute tubuli, which, I believe, represent 
connecting foramina, or “ endosarcal passages,’ as Mr. Vine calls a 
similar feature in the Stictoporide and Ptilodictyonide.. The tubes 
at first are thin-walled, and prostrate. Just as they are about to assume 
an erect position, they are more or less constricted, or cut in two, by an > 
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