PREFACE 



The present volume includes the letter press and plates which constitute a 

 portion of Volume V, Part 1, of the Palaeontology 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 woi-k 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 descrijitions and figures of the species under the genera included 

 in the accompanying synopsis, belonging to the families, Pectenida?, Pterinida^, 

 Aviculidae, Ambonychidse, and Mytilida3. 



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 Rei^orts 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. 



