American Paleozoic Bryozoa. 85 
The species of Dekayia alluded to, has flattened branches and distinct 
macule of smaller cells, and the only well marked feature, shown in 
thin sections, wherein it differs from H. subpulchella, is found in the 
larger size and smaller number of the spiniform tubuli. Precisely the 
same difference distinguishes H. solitaria from another undescribed 
species of Dekayia. Despite the close resemblance between several 
species of the two genera, I believe that they should be held separate 
and distinct. I have been strengthened in this belief, after a 
eareful examination of all the species of the two genera known 
to me, by finding a character that pertains in a more or less marked 
manner to all the species of Dekayza, but which I have sought for in 
vain in species of Heterotrypa: namely in species of Dekayzia, at 
certain periods in the growth of the zoarium, a thin pellicle is drawn 
over greater or smaller patches of the surface, while other portions of 
the surface have the cell-apertures open. This covering being thin 
and delicate, is of course only to be observed in well preserved 
specimens. I have no doubt that the pellicle was developed at the 
close of the existence of the zooids of each layer of cells, so as to form 
the floor of the succeeding layers, and ultimately the diaphragms 
which cross the tubes. 
As asummary of the preceding remarks, it may not be out of place 
to subjoin a description of HeTerorrypa, based upon the aggregate of 
characters shown by the different species known to me. 
Zoarium growing from an expanded base, attached to foreign objects, 
upward into simple, often undulated or irregularly inosculated fronds, 
and occasionally into flattened branches. Cell-apertures varying in 
shape from polygonal to circular, They are separated from each other 
by walls or interspaces, which may be comparatively thin (H. solita- 
ria), or nearly as thick as their own diameter (H. vaupeli). Intersti- 
tial cells from few to very numerous, always angular or subangular. 
Spiniform tubuli small, usually numerous (sometimes excessively so, 
as in H. vaupelz), occasionally inflecting the walls, and giving the cell- 
apertures an irregularly petaloid appearance. Internally we find that 
the walls of the tubes are more or less thickened as they enter the 
“mature” reyion, and apparently amalgamated with one another. The 
diaphragms are straight, of one kind only, more numerous in the in- 
terstitial tubes than in the proper zooecia, and always more crowded 
in the “mature” regions than in the “immature” or axial region. 
HETEROTRYPA VAUPELI, 0. sp. (PI. I. figs. 2, 2a, and 20.) 
Zoarium very irregular in its growth, forming twisted, and always more 
