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. Among 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, 
