58 
CORRELATION OF GEOLOGICAL FAUNAS. 
[bull. 210. 
Table Ilia. — Dominant eastern species not dominant in the Eighteenmile Creek 
section. 
Spirifer granulosus 10 
Chonetes coronatus 6 
Palseoneilo constricta 4 
Nuculites triqueter 1 
Nucula bellistriata . 
Nucula corbulif ormis . 
There are also several species in the range list of Eighteenmile 
Creek not in the dominant distributional list of eastern New York. 
They are: 
Table Illb. — Dominant Eighteenmile Creek species not dominant in the eastern ? 
New York region. 
HBfaun- 
ules. 
146 faun- 
ules. 
Chonetes lepidus 
C. scitulus .- 
Primitiopsis punctUifera 
Stropheodonta perplana ... 
11 
17 

IT) 
Orthothetes arctistriatus 
Rhipidomella vanuxemi 
Productella spinulicosta . . 
Cryphaeus boothi. 
12 
17 

17 
The numbers in this list indicate the number of times the species 
is recorded among the J 40 fail miles of the eastern distribution recorded 
by Prosser; these numbers indicate that the species are rare in the 
East. 
It is evident, therefore, that the Hamilton fauna of western New 
York is considerably modified from the standard presented in eastern 
New York. 
CONSTRUCTION OF A STANDARD LIST OF THE DOMINANT 
SPECIES OF THE TROPIDOLEPTUS FAUNA. 
These several local lists already presented may be assumed to give 
a fair representation of the dominant characteristics of the Tropido- 
leptus fauna, derived in two ways — first, on the basis of frequency of 
occurrence in geographical distribution for a region in which the for- 
mation is typically expressed ; second, on the basis of frequency of 
recurrence of the species in vertical range through the successive 
zones of a continuous section, passing from the bottom to the top of 
the formation. 
The statistics in all cases were prepared with special attention to 
the discovery of the facts used in the present discussion, and by men 
who were well acquainted with the fauna they were analyzing. 
Difference of opinion regarding the identification of species is not 
alone due to difference in knowledge. The same person is more likely 
to use specific names alike in successive papers, but the habit is not 
uniform, as statistics show. Nevertheless, for determining values of 
species in terms of abundance or frequency of occurrence, lists made 
