DEVELOPMENT OF SOME SILURIAN BRACHIOPODA 311 



use of a large proportion of the species as a means of study- 

 ing 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 establishment of numerous specific and generic sj'nonyms. 

 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 misconception of the 

 full significance of age, sex, habitat, and condition of preser- 

 vation. Additional confusion often results from the inclu- 

 sion, 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 peculiarities arising 

 from accident, disease, and impoverished conditions. 



In the case of rare species, or of meagre 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 specimens 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 some conception of 

 its size may be obtained from the fact that, when received, it 

 weighed about seven tons. At the time mentioned all the 

 mature specimens were selected and specifically separated. 

 Many immature forms were also reserved and used in arrang- 

 ing the series prepared for exhibition in the State Miiseum. 

 It was designed to represent in the arrangement each species 

 by a series of specimens showing the gradations of size and 



