PREFACE. XI 



Our manuscript was prepared three years ago ; and its pub- 

 lication delayed in order to provide the illustrations. The 

 rapid advance of the science, during this brief period, ren- 

 dered it necessary that we should re-arrange, and re-write, a 

 large portion of it. 



Copious materiel exists toward the remaining OLOGIES of 

 the Natural History of Chester County. Who will undertake 

 the task of making the necessary selections, and giving them 

 to the public ? 



