OF DENISON UNIVERSITY. 
171 
surface is concave, corresponding to the convex outline of the upper 
surface. Cells of about the same size, occasionally a few are 
slightly larger in size, but form no distinct feature in the 
growth of the zoarium. Cell apertures polygonal, but rounded and 
almost circular, having a tendency to arrange themselves in rows. In 
the space left between the outlines of four cells is usually an angular 
interstitial cell not always readily recognized at the surface under a 
low magnifying power. Cells with cystoid diaphragms along one side, 
the ends of the same gradually becoming attenuated and almost meet- 
ing on the other side of the wall, thus almost encircling the cells. In 
addition to cystoid diaphragms a number of straight diaphragms are 
found, which run from the middle of the cystoid diaphragms to the 
opposite wall. The interstitial cells are also crossed by straight dia- 
phragms, which, however, are far more numerous than those of the 
regular cells, being usually twice as many or even more. 
Cells, about 8 or 9 in a distance of 2 mm ; in one specimen 
about 18 straight diaphragms are found in the length of an interstitial 
cell, 9 cystoid diaphragms are found in the adjoining cell, most of 
which are connected with a straight diaphragm also belonging to this 
cell ; since the thickness of this specimen is about i mm, a very fair 
idea of the relative importance of these tissues may be formed. Ex- 
pansions vary from 20 mm. to 33 mm. in diameter. The name signi- 
fies <2 little shield. 
Locality and position. Huffman’s Quarry, Beavertown Marl; 
Soldiers’ Home, Clinton Group. Todd’s Fork, in the upper iron-bear- 
ing portions of the Clinton Group; this iron-containing layer, which 
is here several feet thick, contains almost all the characteristic fossils 
of the Beavertown marl. 
Genus MONOTRYPELLA, Ulrich. 
“ Ramose, smooth or tuberculated. Cells apparently of one kind 
only. Walls very thin in the axial portion of the branches, but thicker 
in the peripheral region. Diaphragms straight. No spiniform tubuli.” 
(Ulrich, Am. Pal. Bry.) The following species is provisionally re- 
ferred here on account of the apparent absence of interstitial cells. 
