American Paleozoic Bryozoa. 83 
one tube-diameter distant from each other. The funnel-shaped, dia- 
phragms noticed in the preceding species (A. cingulata), are much more 
numerous in this species. Not infrequently two or three open into each 
_ other in such a manner that by the coalescence of the contracted parts of 
the superimposed funnels, a smaller irregular tube is formed within the 
proper tube-cayity. As is shown in fig. 16, these diaphragms in their 
normal condition are represented in the section by two thin converging 
lines, springing from the walls of the tubes, and nearly meeting near 
the center of the tube cavity. Frequently, however, one of these lines 
is missing. In this case the diaphragm extends from one wall nearly 
across the tube toward the opposite wall. 
Superficially, the species above described resembles the type of the 
genus, though not nearly enough to be confounded with it by one ex- 
perienced in the determination of this group of fossils. The cell- 
walls are thinner, and the groups of large cells more conspicuous in 
A. robusta than in A. cingulata. Internally, the comparatively thin 
cell-walls and numerous funnel-shaped diaphragms, and the small 
number of spiniform tubuli of A. robusta will further distinguish it 
from that species. Care must be taken in separating the species from 
Monotrypella equalis, Ulrich, which the smaller specimens of A. ro- 
busta strongly resemble. The former, however, is restricted to the 
lower 150 feet of the strata exposed at Cincinnati, O., while the latter 
is limited to a few feet of strata at least 225 feet higher in the series. 
Formation and locality : Cincinnati Group. Rather rare near the 
tops of the hills about Cincinnati, O. 
Heterotrypa, Nicholson. 
Of the seventeen species placed under Heterotrypa by Nicholson 
(«The Genus Monticulipora’’ 1881), but two are, according to my 
opinion, congeneric, viz. : the type species, H. frondosa, D’Orb. (H. 
mammulata, Nich.), and H. subpulchella, Nich. Of the remaining 
fifteen, H. andrewsi, Nich., H. nodulosa, Nich., H. sigillaroidea, Nich., 
F. ramosa, D’Orb., and H. dalei, Ed. & H., must be referred to Callo- 
pora, Hall; A. barrandi, Nich., and H. moniliformis, Nich., to Am- 
plexopora, Ulrich; H. dawsoni, Nich., to Homotrypa, Ulrich ; H. gir- 
vanensis, Nich., H. implicata, Nich., and H. jamesz, Nich., to Batos- 
toma, Ulrich; H. gracilis, Nich., and H. tumida, Phill., to Batosto- 
mella, Ulrich ; and H. trentonensis, Nich., to Monotrypella, Ulrich. 
The type species of Heterotrypa is a common, easily recognized, and 
well known fossil of the Cincinnati group, and its characters have 
