williams] BIONIC VALUE OF FOSSILS. 131 
REVISED DEFINITIONS OF THE TERMS FAUNA AND FAUNULE. 
The term fauna is commonly used in paleontology to indicate the 
list of fossils contained in a single formation, but it is important to 
observe that the limits of the lithological formation do not determine 
the limits of the fauna. It will be seen from the discussions of faunas 
and faunules in this paper that a new definition of a fauna is require* 1 
which shall not be dependent upon formation boundaries. The fol- 
lowing points should be included in such a definition : For paleon- 
tology a fauna is an aggregate of local and temporary faunules in 
which is expressed a common, corporate aggregate of organic species. 
The corporate nature of the aggregation is indicated by the relative 
bionic values maintained b}~ the species in the faunal aggregate. 
The dominant species of a fauna show their relation to the fauna by 
their higher bionic values, the less dominant species by their low 
bionic value, and the fauna shows its integrity by maintaining the 
normal equilibrium of the specific aggregates. The Tropidolejitus 
carinatus fauna is defined in this report as an example of such a 
fauna. 
In the process of collecting fossils it is necessary to keep separate 
records of the specimens taken from each fossiliferous stratum of 
each separate outcrop. The group of specimens from such a unit 
stratum (or from several contiguous strata in which the same set of 
species are distributed) is called a faunule. It is a sample of the 
general fauna of the formation, coming from a definite horizon in the 
local section and from a definite geographical position. A faunule wi 1 1 
exhibit the local and temporary aspects of the fauna, and in most 
cases it will contain only a small part of the species which properly 
belong to the general fauna. The faunule may be regarded as closely 
ad justed to a particular set of environmental conditions, which, 
though not known, may be to some degree inferred by the character of 
the sediment in wliich it is found. It is often observed, however, 
that successive faunules in a column of strata differ greatly, although 
very slight change in character of sediments is observed. Living 
faunas in modern ocean waters so differ on account of differences of 
temperature or other conditions of the water, and it may be supposed 
that such differences affected in a similar way the ancient geological 
faunas. 
The particular part of the formation, be it a single stratum, or a 
few or many feet of thickness of rock throughout which the faunule 
is recognized is properly a zone, as defined on page 20; and the 
locality, number, and name may be applied to the specimens of the 
faunule, as well as to the stratum or strata from which they came. Bui 
the faunule is the faunule of such a zone, and its proper name should 
be derived from the name of some dominant species (as Leiorhynchus 
globuliforme faunule or Paracyclas Virata faunule) when the analysis 
