XIV 
PREFA CE. 
leaving for those who may come after him the pleasure and satisfaction of 
producing a more complete work. Notwithstanding all these difficulties, the 
author is willing to believe that the students in geology will thank him for 
presenting to them, in the best dress possible, the imperfect material which 
would otherwise remain unavailable in their collections, and of no value to 
science or to scientific museums. 
The species described in this volume are illustrated by figures drawn and 
lithographed from original specimens, which are chiefly in the State Museum - 
collections, derived either from the original Geological Survey or from subse¬ 
quent acquisitions; together with collections made by myself, or under my 
direction, and of specimens obtained from other authentic sources. 
The order and succession of the species, as presented in the plates of 
Gasteropoda, may not be strictly that which a systematically arranged con- 
chological collection might require; but it is in accordance with the intention 
of the author, except in the few supplementary plates, and will be found to 
present a simple and natural order, so far as external form is concerned. 
In the Cephalopoda, the author has preferred to begin with the simple Ortho- 
ceratites, and to follow with those which present an external gradation of 
form, through the genera Gomphoceras, Cyrtoceras, Gyroceras, Trochoceras, 
Nautilus and Goniatites. Unfortunately, the earlier lithographed plates were 
arranged with a very incomplete knowledge of the material contained in the 
State collections, and this has necessitated the introduction of the simpler forms 
on the plates following the completion of the first arrangement, or from plate 74, 
ending with the Goniatites. This want of unity could not be avoided, but it 
affects only the plates—the text presenting the genera and species in consecu¬ 
tive order from page 217 to the end of the volume. 
In the preparation and final revision of the descriptions of the species of 
Cephalopoda I have been very ably assisted by Mr. C. E. Beecher, and in the 
proof-reading and preparation of the index to the volume I am indebted to 
Mr. J. A. Lintner. 
For the use of specimens in the study and illustration of the work I have 
been indebted to Prof. S. G. Williams, of Cornell University, from his private 
