American Paiwozoic Bryozoa, 87 
represents a portion of a section somewhat intermediate between the 
two phases described. 
Longitudinal sections (Pl. I., fig. 2b) show that the ee in the 
axial region have very thin did somewhat flexuous walls; that they 
approach the surface gradually, that the peripheral or “ mature” belt 
on each side of the frond is very narrow, and, as they enter the latter 
region, that their walls are thickened. In the proper zooecial tubes the 
diaphragms are usually wanting throughout the axial region, and they 
are never numerous even in the peripheral portion of the zoarium. In 
the interstitial tubes they are numerous, and generally very thick. 
In its internal structure this species is very remarkable, and differs 
widely from H. frondosa. One peculiarity in its structure I can as 
yet not fully understand. That the interstitial cells are actually sup- 
pressed as the zoarium becomes fully matured, I must doubt. I would 
‘rather believe that the spiniform tubuli, which are developed in the 
spaces that in the earlier stages of the growth of the zoarium were occu- 
pied by interstitial cells, have sprung from the surface of diaphragms 
which covered the interstitial cells. Iam upheld in this belief by find- 
ing, what appears to me to be, corroborative evidence: namely, on many 
diaphragms of the interstitial tubes, I can detect one or two, rather 
faintly delineated, hollow processes, extending upward from the dia- 
phragm toward the one next succeeding. If this is not deceptive, then 
we have a curious analogy with such more recent Bryozoa as Hetero- 
pora pelliculata, Waters (a recent species), in which the orificed of the 
interstitial cells are closed by a perforated pellicle. The only differ- 
ence (as regards this point) between such forms and H. vaupelt, being 
that in the latter the surface of the pellicle or diaphragm is elevated 
into a hollow spine, instead of being perforated by a simple foramen. 
Examples of H. vaupeli are readily distinguished from all the fron- 
descent Monticuliporide described from the Cincinnati group, by their 
peculiar growth, circular cell-apertures, and regular arrangement of 
the cells and monticules. When in a good state of preservation the 
most striking characteristic is found in the granular cell interspaces. 
The name is given in honor of my esteemed friend, Mr. E. H. Vau- 
pel, who is an enthusiastic student of Paleozoic fossils. He has not 
only gathered one of the best collections of the Cincinnati group 
Bryozoa, but he is also able to classify them. 
Formation and locality: Cincinnati group. Not uncommon near 
the tops of the hills about Cincinnati, O. It is associated with, and 
apparently restricted to the same beds as Amplexopora robusta. I 
