PREFACE. 



The present publication constitutes the Second Part of Volume V of the 

 Palaeontology of New York. The volume contains descriptions and illustra- 

 tions of the Gasteropoda, Pteropoda, and Cephalopoda of the Upper Helderberg, 

 Hamilton, Portage, and Chemung groups. It was originally intended to include 

 all the Mollusca of the classes Lamellibranchiata, Gasteropoda, Pteropoda and 

 Cephalopoda of the above groups in a single volume ; but a yet unfinished study 

 of the first class has required eighty plates for its proper illustration, and for 

 its final revision and completion several more plates will be necessary. The 

 three other classes are here illustrated in one hundred and twenty plates, which 

 still leaves some of the material in our collections unrepresented. Amono- the 

 Cephalopoda a large proportion of the material is fragmentary and in the 

 condition of casts of the interior, rendering the study more difficult and the 

 illustrations far less satisfactory. Reference to this subject may be found in 

 some remarks preceding the descriptions of the Orthocerata, and the same 

 observations are applicable to all the Cephalopoda of the Schoharie grit. We 

 are compelled to use such material, or to leave the species unillustrated for an 

 indefinite period. The limestones of the Upper Helderberg and the shales of 

 the Hamilton group afford more satisfactory material ; but in the Portage and 

 Chemung groups the collections are very fragmentary and unsatisfactory, and 

 the results of the most careful study still leave much to be desired. Under 

 these circumstances an author would prefer to wait for more complete collec- 

 tions ; but the public are unwilling to appreciate this sentiment, and the State 

 authorities, who represent the public, demand publication. It therefore only 

 remains for the author to give the best results he has been able to obtain, 



