X 
PREFACE. 
The collections for the illustrations of this volume have been chiefly made 
by myself and by assistants formerly occupied in collecting material for the 
Palaeontology of the State, and later by assistants connected with the State 
Museum. Collections have been purchased by the author from Mr. Edmond 
De Cew, and of the late Mr. John De Cew, of Cayuga, Ontario, Canada; the 
latter having also made special collections for use in this work from the siliceous 
layers of that part of the Helderberg group in Canada. This work is indebted 
to Mr. Victor W. Lyon, of Jefferson, Indiana, for important collections made 
at the Falls of the Ohio. These specimens were in a perfectly preserved con¬ 
dition, and have constituted an important element for the illustration of this 
volume. 
The original drawings have all been made by Mr. George B. Simpson, who 
has critically studied all the species, and, with the appreciation of a naturalist, 
has faithfully represented the delicate structure of these organisms in the 
illustrations accompanying this volume. Credit is due him for the preparation 
of a large part of the specific descriptions. In the execution of the drawings 
Mr. Simpson has shown the same artistic ability which has characterized his 
previous work. 
The lithography has been chiefly done by Mr. Philip Ast, of whose ability 
in reproducing the original drawings upon stone, we cannot speak too highly. A 
few plates by the late Mr. H. Bergmann, give very accurate and elaborate repre¬ 
sentation of Favosites Helderbergm and of species of Fistulipora, Ptilodictya, 
etc., of the Lower Helderberg group. More recently some plates of the Upper 
Helderberg and Hamilton groups have been done by Mr. Paul Riemann. 
We are indebted to Mr. Charles E. Beecher for the preparation of the Synopsis 
of the Genera and Sub-genera described and illustrated in this volume ; and also 
for the arrangement of the explanations of plates, with references to the pages 
of the volume and the localities of the species. 
Mr. Beecher and Mr. Simpson have rendered assistance in proof-reading while 
the volume has been passing through the press. 
THE AUTHOR, 
Albany, August, 1887. 
