CORALS AND BRYOZOA. 
225 
Fistulipora spiieroidea. 
PLATE LVII, FIGS. 3, 4. 
Thallostigma spiieroidea, Hall. Trans. Albany Institute, vol. x, p. 187. 18S1. 
“ “ “ Report of State Geologist for 1883, p. 31. 1884. 
Zoarium usually consisting of spheroidal masses formed by the accretion of 
successive layers of growth; diameter of the largest specimen observed 
45 mm., thickness of each layer from 2 to 10 mm. Cells tubular, cylindri¬ 
cal, in the thinner fronds curved, in the thicker fronds straight and at right 
angles to the surface for nearly their entire length; septa very infrequent 
and in many of the tubes entirely wanting. Intercellular tissue usually 
consisting of irregularly disposed vesicles, but where the cells are very near 
each other, they are regularly superimposed, appearing as septate tubuli, 
twenty-five-or thirty septa in the space of 5 mm. Cell apertures circular or 
sub-polygonal from mutual pressure, closely and irregularly disposed, usu¬ 
ally some portion of the margins in contact with adjacent cell apertures. 
Peristomes thin, distinctly and equally elevated, when well preserved hav¬ 
ing numerous short spinules. Interapertural space occupied by minute 
mesopores, which partially or entirely surround the apertures, frequently 
appearing like the interstitial cells of a Ch/etetes. Surface without mon¬ 
ticules or maculae. 
The generally spheroidal form of this species will distinguish it from others 
of the genus Fistulipora, with the exception of F. unilinea and F. hemispherica; 
it bears a very close resemblance to the former, but may be distinguished by 
its somewhat larger cell apertures, their more crowded appearance, the spinules 
on the peristomes and the absence of maculae destitute of cell apertures: 
from the latter by the circular or sub-polygoual cell apertures, their crowded 
arrangement, and the much smaller mesopores ; in some conditions it is similar 
to F. ponderosa of the Lower Helderberg group, but the cell apertures are 
larger and the mesopores fewer in number; where the surface is well pre¬ 
served the difference is more apparent: from F. constrida it is distinguished by 
