20 PREFACE 



Especial acknowledgment is due to Dr. John M. Clarke, Director of the 

 New York State Geological Survey, not only for advice and assistance, but 

 for the use of a large number of drawings first employed in the classic 

 volumes on the Paleontology of New York. 



The authors are also greatly indebted to Dr. Edward 0. Ulrich of the 

 United States Geological Survey for his constant interest in the progress 

 of the work and his very material assistance in connection with many 

 disputed points in the discussion. Dr. Ulrich and Dr. R. S. Bassler, of the 

 United States National Museum, have also prepared the systematic por- 

 tions relating to the Bryozoa and Ostracoda. 



