584 



HENRY SHALER WILLIAMS 



Era. — May be used to indicate a tetrabiochron ; and Olenide era would 

 indicate the life range of the family Olenidae, corresponding in length, 

 approximately, to the geochron of the Cambrian system, though not 

 strictly so. 



Eo7t. — May stand as the name for a pentabiochron ; an example of which 

 is the Trilobite eon, the time equivalent of the continuance of the order, or 

 sub-class, Trilobita, which closely approximates the length of the Paleozoic 

 g-eochron. 



CLASSIFICATION AND NOMENCLATURE OF THE 

 (paleozoic) constructed on the BASIS 

 VALUES OF FOSSILS. 



TRILOBITE EON 

 OF THE BIONIC 



Eon 



Periods 



Trilobiteon ' 



7. Phillipsian 



6. Phacopsian 



5. Calymenean 



4. Asaphian 

 3. Olenian 

 2. Paradoxidean 

 I. Olenellian 



Epochs 



r Cameratus - 

 I Increbescens 

 Logani - 

 Marionensis 



Disjunctus - 

 Mucronatus - 

 < Acuminatus - 

 Arenosus 

 Macropleurus - 



Vanuxemi - - 

 Radiatus 



? 



Formational Equivalents 

 (Approximate) 



Coal measures. 

 Kaskaskia, St. Louis. 

 Keokuk, Burlington. 

 Kinderhook. 



Chemung. 



Hamilton. 



Corniferous. 



Oriskany. 



Lower Helderberg. 



Waterlime, etc. 

 Niagara, etc. 

 Ordovician. 



Cambrian. 



Applying the principles set forth in this paper, a tentative 

 table may be constructed which will express concretely what is 

 meant by a biochronic classification and nomenclature. In this 

 table the attempt is made to find names of genera of Trilobites 

 for the periods of that eon in which Trilobites constitute a 

 characteristic feature. The genera chosen actually do lap over 

 each other in several places, but it is doubtful if any genera 

 could be chosen which, if they did not lap over in their chrono- 

 logic range, would leave actual gaps not represented in any divi- 

 sion of the scale. The genus Spirifer is selected in the upper 



