268 Cincinnati Society of Natural History. 
nature as the similar structures which mark the fully matured stage 
of Pachydictya, Cystodictya, and many of the Fistuliporide. Figure 
2e represents the appearance of the cells in the inter-monticular spaces, 
at a level nearer that represented in fig. 2d, than 2c. 
Longitudinal sections (Pl. XIV., fig. 2/) show that the axial region 
is occupied by rather large and excessively thin-walled tubes, in which 
diaphragms are almost entirely absent. As they approach the surface, 
they bend outward abruptly, and here a large number of rapidly expand: 
ing interstitial tubes are developed, in which horizontal diaphragms 
recur at diminishing intervals, until at the surface they are crowded. 
The diaphragms as a rule are complete, and occupy the same level in 
contiguous tubes. Sometimes those cressing one of the large tubes 
(interstitial) are incomplete, and appear to form a vesicular tissue. As 
this, however, has not been noticed in the other species of the genus, I 
am inclined to regard the feature as probably due to accident, though 
I am not disinclined to the belief that it perhaps is also predictive: 
The interstitial tubes would almost appear to have been reproduced by 
fission, but this is evidently not the case, as in tangential sections, par- 
tially divided cells are never met with, and such would doubtlessly be 
of common occurrence, had the method of reproduction been fissipar- 
ous. This false appearance is due to the fact that the young intersti- 
tial tube, like those first developed, enlarges very rapidly, often attain- 
ing its full dimensions before it is crossed by the first diaphragm. In 
the section figured, the outer layer of interstitial cells is clear, while 
several just below it are filled with a deposit of sclerenchyma. This I 
believe is due to the filling of previous layers of cells, by the zooids of 
the next succeeding layer. 
This species in its typical form, represented by fig. 2, on Plate XIV., 
is a common fossil in the Cincinnati group. It seems to range between 
250 and 400 feet above low water mark in the Ohio river, at Cincinnati, 
Ohio. Figure 2a represents a portion of an example of this species, 
on which the monticules are remarkably elongated transversely. This 
variation from the typical form is of common occurrence, but of very 
little importance, since on other portions of the same specimen the 
monticules are like those of fig. 2,ip form, size and distribution. An 
exactly parallel case is found in the transverse elongation of the mon- 
ticules of Callopora ramosa, D’Orb., going to make the variety rugosa 
(Chetetes rugosus, Ed. & H.) Figures 3 and 4 represent two varieties, 
which are sufficiently marked by their external characters to render 
their separation from the more typical forms of the species usually an 
