Acervularia Profunda and Davidsoni.— Calvin. 357 
superiority in size of A. profunda may not be maintained in all 
localities. In the Paleontology of Ohio, Vol. 11, page 240, Dr. 
Nicholson describes a form under the name of <Acervularia pro- 
funda Hall, that is distinguished among other things by having 
the corallites smaller than in A. davidsont. 
The shape of the calyx is markedly different in average speci- 
mens of the two species. In A. profunda the calyces are sepa- 
rated by relatively thin partitions owing to the manner in which 
the sides of the cup slope abruptly downward and inward from 
the margin; the septa are thin and have conspicuous, crowded 
carinz which are as fully developed near the margin of the calyx 
as around the central area, particulars in respect to which they 
are in marked contrast with the septa of A. davidsoni. The 
septa differ still further from those of A. davidsoné in having more 
of their edges free and in having their edges beautifully dentic- 
ulated. There is but little thickening of the septa to form a 
pseudo-wall around the central area; indeed this feature is, in a 
very large proportion of cases, wholly wanting. The secondary 
septa are nearly as long as the primaries and often become coa- 
lesced with the primaries inside the central area. 
Acervularia davidsoni Kd. and H., has a much wider geo- 
graphical range in lowa than A. profunda Hall. The area in 
which A. profunda occurs is nearly all included in parts of Buch- 
anan and Blackhawk counties, while the area over which the 
other species is distributed is many times greater. As pointed out 
in the GEoLoais? for September, 1891, A. profunda is not associated 
in the same beds with A. davidsoni, but occurs uniformly at a hori- 
zon a few feet lower. Outside the area occupied by A. profunda its 
place seems to have been taken by Phillipsastrea gigas Owen. At 
least this last species, while never very common, occupies the same 
relative position a few feet below the horizon at which A. david- 
soni is found, and so far as known it is not present in the region 
in which A, profunda attains its maximum development. 
With respect to the particulars in which A. profunda differs 
from A. davidson? it agrees essentially in structure with Cyatho- 
phyllum rugosum of authors, and it may therefore be regarded as 
the western representative of the last named species. If cari- 
nated septa have any generic significance, then Cyathophyllum 
rugosum is certainly not a Cyathophyllum at all. Whatever may 
be the significance of the carina and other peculiarities of struct- 
