PREFACE. 
The present volume includes the letter press and plates which constitute a 
portion of Volume V, Part 1, of the Paleontology of New York. It was 
originally intended to arrange the whole of this material as a volume of text 
and a volume of plates ; but the exigencies of publication have made it necessary 
to issue a volume of the work at the present time, and in its present form, leav¬ 
ing the remaining portion to constitute a similar volume which will be published 
early in the next year. 
The entire work will embrace the descriptions and figures of all the recognized 
forms of Lamellibranchiata from the Upper Helderberg, Hamilton, Portage and 
Chemung Groups within the limits of the State of New York. This volume 
includes descriptions and figures of the species under the genera included 
in the accompanying synopsis, belonging to the families, Pectenidae, Pterinidae, 
Aviculidas, Ambonychidae, and Mytilidae. 
The fossil Lamellibranchiata of the higher groups of the New York geological 
series are often abundant, of great variety of form and of very interesting 
character. Our earlier knowledge of these fossils is almost wholly due to Mr. 
Conrad, who described eleven species in the Annual Report of the Geological 
Survey in 1838 ; and during the following years this work was continued, both 
in the Annual Reports of the Survey and in the Journal and Proceedings of 
the Academy of Natural Sciences of Philadelphia. The total number of species 
described by Mr. Conrad from all the groups is about one hundred and ten, and 
fifty of these have been illustrated in the publications of the Academy. The 
number of species at present known from the same formations is about 600, of 
which nearly 500 are from the groups above the Oriskany sandstone. 
