Williams] FAUNAL DISSECTION OF THE DEVONIAN. 53 
The next two species, Spirifer granulosus and Chonetes coronattis, 
are common 26 times out of 59 and 57 occurrences, respectively. 
The remaining species of the list are occasionally abundant and 
common for from 4 to 12 times out of from 32 to 50 occurrences; or 
something like 20 per cent of the times they were observed they were 
common species in the faunule analyzed. 
In matter of relative dominance among the species of the fauna the 
list is therefore representative, and since all the remaining 160 spe- 
cies of the Hamilton formation of this region (so far as reported in 
these statistics) are both less frequent and less abundant in the 
faunules examined, we may assume that we have here not only the 
dominant but the characteristic species of this Tropidoleptus carinatus 
fauna. 
This set of statistics was chosen for first consideration for the fol- 
lowing reasons: 
(1) The localities are distributed over a considerable territory, so 
that in case there were local peculiarities in the samples of the fauna 
examined they might be detected and eliminated. 
(2) Although the fauna can be traced upward in the strata above 
the place of the Genesee formation, in the greater part of this region 
the pure Chemung fauna does not appear in the series above the 
Hamilton fauna, but its place is represented by the sediments of the 
Catskill, without a strictly marine fauna. 
(3) The faunas are all gathered and studied by a single person; 
hence the personal difference in estimating specific values and identi- 
fications is eliminated, and whatever may be the possible error in 
identification it is likely to be uniformly made, so that as bionic units 
the species may be regarded as fairly uniform in value, the same name 
standing for the same fossil form in each case reported. 
(4) From the general distribution of the Hamilton formation, I 
have estimated that this northeast corner of the Appalachian prov- 
ince is likely to present its fauna in greater purity than it appears 
elsewhere in the interior continental basin. 
(5) The statistics are gathered and studied with great care by one 
thoroughly familiar with the species and keenly aware of the impor- 
tance of making accurate analyses of the faunas. 
I believe, therefore, that the statistics are as reliable as any that are 
published, and that they represent, as accurately as can possibly be 
reported at the present stage of knowledge, the essential elements of 
the fauna of the Hamilton formation. 
RANGE VALUES OF THE SPECIES. 
In order to define a fossil fauna it is not sufficient to enumerate the 
list of species which have been described from the same geological 
formation, chiefly because in such a list will be found species from 
many different regions and from rocks of different stratigraphical 
