WILLIAMS. 
BIONIC VALUE OF FOSSILS. 
133 
Era.— May be used to indicate a tetrabioehron; and Olenide era would indicate 
the life range of the family Olenidce, corresponding in length, approximately, to 
the geochron of the Cambrian system, though not strictly so. 
Eon. — May stand as the name for a pentabiochron; an example of which is the 
Trilobit e eon, the time equivalent of the continuance of the order, or subclass, 
Trilobita, which closely approximates the length of the Paleozoic geochron. 
Classification and nomenclature of the Trilobite eon (Paleozoic) on the 
the bionic values of fossils. 
of 
Eon. 
Period. 
Epo<-k. 
Formational equivalent 
(approximate). 
• 
f Cameratus 
Coal Measures. 
«, 
Phillipsian 
Increbescens 
Kaskaskia, St. Louis. 
Logani _ . _• _ _ 
Keokuk. Burlington. 
Kinderhook. 
Marionensis 
Disjunctus 
Chemung. 
Mucronatus 
Hamilton. 
6. 
Phacopsian 
Acuminatus 
Corniferous. 
Trilobite 
Arenosus 
Macropleurus 
Oriskany. 
Lower Helderberg 
Calymenean 
/ Vanuxemi 
1 Radiatus 
Waterlime, etc. 
.1. 
Niagara, etc. 
4. 
Asaphian 
(?) 
Ordovician. 
3. 
Olenian 
) 
2_ 
Paradoxidean 
(?) 
Cambrian. 
U- 
Olenellian 
Upon reviewing the subject I am of the opinion that this table 
fairly expresses the difficulties to be encountered in applying the 
principles here set forth as well as the advantages. When the 
table was constructed the details of the present paper were not 
ready for presentation. I am able now to point out the method of 
application to the Devonian faunas which have been already sub- 
jected to analysis. 
The several faunas under consideration are the measures of epochs 
according to this scheme. We have thus: Tropidoleptus carinatus 
epoch, Glyptocardia speciosa epoch, Prod urf din speciosa epoch, Spiri- 
fe i - d isj u net us epoch . 
Regarding these faunas and the time epochs indicated by them, it 
has been demonstrated that the range of time indicated by each epoch 
is not restricted to the particular formational limits in which the fauna 
is typically confined. 
The Tropidoleptus epoch laps over both of the following two and 
reaches to the beginning of the fourth. The epoch of I he Glyptocardia 
speciosa fauna is prior to and follows the limits marked by the typical 
Productella speciosa fauna at Ithaca. 
The Spirifer disjunctus fauna, though in general Later than the 
other three faunas in the New York province, probably dates its 
origin from a much earlier stage outside that province, into which it 
most probably came by migration, and not as an evolution from the 
earlier inhabitants of the New York province. 
