6 ' INTRODUCTION 



with geologists having more or less of a zoological training, and the prin- 

 cipal aim has been to present the faunal aspects of each horizon for the 

 purpose of chronological identification. This process has frequently 

 become so involved with the imperfect description of species, that the 

 systematic zoologist or paleontologist is unable to make any use of a large 

 proportion of the species as a means of studying their taxonomic relations 

 or their structural affinities with each other and with recent forms. 



Each revision of a group of fossil animals has resulted in the establish- 

 ment of numerous specific and generic synonyms. Many of these are 

 owing, of necessity, to the imperfection of the material, and many names 

 which are finally relegated as synonyms, have been created under a mis- 

 conception of the full significance of age, sex, habitat and condition of 

 preservation. Additional confusion often results from the inclusion, in a 

 generic or specific description, of characters which pertain not alone to a 

 normal individual, but interspersed with certain normal adult features are 

 those belonging to various stages of morphological development and pe- 

 culiarities arising from accident, disease and impoverished conditions. 



In the case of rare species, or of meager material belonging to common 

 forms, it is to be noticed that assertions regarding specific and generic 

 characters are usually very positive ; while, with an abundance of speci- 

 mens representing many stages of growth and the extremes of individual 

 variation, the descriptions are qualified, the latitude of genera and species 

 is extended, and the points of relationship with allied forms are multiplied, 

 thus binding a group of organisms into comparative uniformity, without 

 anomalous differences such as often occur where the dividing lines are 

 rigidly drawn. 



During the years 1878-79, the collection of fossils made from the 

 Niagara group at Waldron, Indiana, for the New York State Museum, 

 was studied and arranged by one' of the writers. This is probably the 

 largest collection yet brought together from that celebrated locality, and 



