x j v PREFACE. 



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 



