162 Cincinnati Society of Natural History. 
cavity is distinctly shown and comparatively large. Diaphragms are 
usually developed at remote intervals, though often wanting. No 
interstitial tubes have been observed. 
In tangential sections (Pl. VI., fig. 3) the cells are seen to be thin- 
walled and of rather unequal size. Spiniform tubuli of moderate size 
are plentifully developed, placed at the cell-angles and often at points 
between, in which cases the walls are forced into their respective cell- 
cavities on each side. No special series of small cells are observed in 
these sections. 
This species is probably most nearly allied to Z, ornata, from which 
it differs principally in having more numerous spiniform tubuli, which 
are also much more conspicuous, both externally and internally. 
These differences will also apply to the other species. 
Formation and locality: Cincinnati group. A common species in 
the lower 200 feet of strata exposed at Cincinnati, O., and elsewhere. 
LEPTOTRYPA CORTEX, * 0. Sp. 
Zoarium attached to the shells of Orthoceras and EHndoceras, over 
which it forms large expansions, from .02 to .08 of an inch in thickness, 
and several inches in length. Surface smooth, but with distinct 
clusters of cells, larger than the average, at intervals of .15 of an inch, 
measuring from center to center. The cells are moderately thin-walled, 
and quite regularly hexagonal, those of the ordinary size having a 
diameter of about jth of an inch, while that of the largest in the 
clusters rarely exceeds 4th of an inch. 
Longitudinal sections show that the tube-walls, just above the 
epithecal membrane, are very thin; nearer the surface they are some- 
what thickened, and show the line of demarcation separating the walls 
of adjoining tubes, and an occasional spiniform tubulus. Diaphragms 
are quite numerous, those in the upper part of the tube being about 
one half a tube-diameter apart, which distance is gradually increased 
in the lower portion to more than one tube-diameter. Interstitial 
tubes are entirely absent. 
Tangential sections show quite distinctly the divisional line between 
the tubes, while the angles are usually enlarged to admit what I now 
regard as spiniform tubuli. They are generally represented only by a 
dark triangular space, but a few also show a minute central lucid spot, 
*The figures of this species were unfortunately overlooked in preparing the plates for this 
number. Being aspecies of some importance, I was unwilling to strike it out of this connec- 
tion, proposing to make my description valid by figuring its characters in my next installment. 
