356 The American Geologist. June, 1892 
had been employed in a work published in America; for although 
Edwards and Haime’s specimens came from near Jeffersonville, 
Indiana, the description of Acervularia davidsoni appeared in the 
great monograph of the authors, published in France. 
It should be noted that near Jeffersonville, Indiana, there oc- 
curs another form which authors, following the example of Ed- 
wards and Haime, usually refer to Cyathophyllum rugosum Hall, 
The three species mentioued above, as recognized by every one 
who has handled them, are somewhat closely related. Dr. Rom- 
inger in Geology of Michigan, Vol. 11, page 107, is disposed to 
regard them all as but varieties of one species. The Acervularia 
davidsoni, as it occurs in lowa is somewhat sharply defined 
from either of the other two, while A. profunda exhibits a very 
intimate correspondence as to structure with Cyathophyllum rugo- 
sum from the falls of the Ohio. 
Comparing A. profunda with A. davidsonit we may note that it 
differs in the appearance and mode of growth of the corallum, in 
the greater tendency to independent grow h of corallites, in the 
size of the corallites, the shape of the calyx, the thicker, non- 
corrugated wall by which the individual corallites are bounded, 
the almost entire absence of an inner pseudo-wall defining a cen- 
tral area, and the thinner septa with more numerous and more 
conspicuously developed carine. 
The A. profunda is a much coarser looking species than A. 
davidsoni. Its lower surface is never as smooth and flat as is 
that of most coralla of the other species from Iowa. This sur- 
face is traversed radially by the outer corallites which stand out 
as strong transversely wrinkled ridges, sometimes almost entirely 
free from union with contiguous corallites. All the corallites 
show a remarkable tendency to independent growth, so that in 
some specimens a large proportion of the whole number of cor- 
allites stand apart on the upper surface of the corallum from those 
adjacent, and are individually covered externally with an inde- 
pendent epitheca. In certain modes of preservation the corallites 
are even separable into wrinkled, polygonal prisms that exactly 
imitate a very common condition in Cyathophyllum rugosum. 
In the region from which Hall’s type comes, the coraliites of 
A. profunda are on the average somewhat larger than those of A. 
davidsoni. Itis true that the corallites of both species vary with- 
in very wide limits, anl it is therefor: quite possible that the 
