INTRODUCTION 7 



some conception of its size may be obtained from the fact that, when re- 

 ceived, it weighed about seven tons. At the time mentioned, all the 

 mature specimens were selected and specifically separated. Many imma- 

 ture forms were also reserved and used in arranging the series pre- 

 pared for exhibition in the State Museum. It was designed to represent 

 in the arrangement, each species by a series of specimens showing the 

 gradations of size and form from mature individuals down to as young and 

 small specimens as could be found. Abnormal examples, also, were 

 reserved and grouped with them. It was tjje intention of the writers to 

 accompany this memoir with photographic illustrations of these series, 

 representing each species here discussed, but it has not been found wholly 

 feasible, and the illustrations are largely restricted to the presentation 

 of the immature and adult conditions of growth, with the exception of the 

 several series which are given on plate 8. 



The product obtained from washing the slabs, was preserved and 

 passed through sieves to assort the material into different grades of fine- 

 ness. It was found that these washings contained a great number of 

 partially developed shells, and it is from them that the extremely young 

 brachiopods, treated of in the present paper, have been derived. The 

 writers have carefully examined all the residue of these washings and have 

 picked out about fifty thousand specimens, most of which are less than five 

 millimeters in length, and many have a length of not more than one milli- 

 meter. After all the imperfect and badly preserved individuals were 

 rejected, there still remained more than fifteen thousand inchoate indi- 

 viduals. 



The sediments at Waldron consist of fine calcareous shales, weathering 

 into clays. A stratum of Niagara limestone overlies the shales at this 

 locality, but none of the fossils derived from this limestone have been used 

 in the preparation of the present paper, and so far as known, it has a com- 

 paratively different fauna and does not furnish such material as is here 



