ACKNOWLEDGMENTS 



The writer wishes to express her indebtedness to Dr. J. A. Bow- 

 nocker, State Geologist of Ohio, for a position on the Geologic Survey 

 of Ohio while the necessary field work was being carried on, and for 

 the many helpful suggestions which he has given her concerning the 

 work. She is likewise much indebted to Mr. Wilber Stout of the 

 Geologic Survey of Ohio, not only for his aid in the collecting of fossils 

 and for the suggestion of localities where collections could be made, 

 but also for his help with the stratigraphy of the Pottsville formation 

 and for the kindly interest which he has taken in every phase of the 

 work. It is a great pleasure to the writer to acknowledge her obliga- 

 tion to Dr. George H. Girty of the United States Geological Survey 

 for the valuable assistance which he has so freely given in the verifica- 

 tion of new species and of obscure or doubtful forms. The writer 

 wishes to thank Mr. Raymond E. Lamborn by whom the collections 

 of fossils from Stark and Mahoning counties were made, Miss Char- 

 lotte Morningstar for her assistance in collecting fossils, and Dr. 

 Florence Bascom and Mr. M. H. Bissel of Byrn Mawr College for 

 reading and correcting the manuscript. 



