INTRODUCTION. 



The fossil Lamellibranchiata, of the higher groups of the New York geological 

 series, are often very abundant, of great variety of form, and extremely interest- 

 ing to the student, when once he has acquired a moderate degree of knowledge 

 regarding their general character and their relation to existing forms. The 

 study of this class of fossils in New York was begun more than forty-five 

 years since by Mr. T. A. Conrad, who was commissioned as Palaeontologist of 

 the New York Geological Survey in 1837, and our earlier knowledge of these 

 fossils is almost wholly due to him through his publications in the Annual 

 Reports of the New York Geological Survey and the Philadelphia Academy 

 of Natural Sciences.* 



In his first Annual Report, " on the Palaeontological Department of the 

 Survey," published in 1838, Mr. Conrad described eleven species of Lamelli- 

 branchiate shells. During the following years, until 1842, 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 formations from the 

 Trenton limestone to the Waverly group inclusive, 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 and described from the same forma- 



* Ml-. C»iii-a(l had ali-eaiiy, in 1835, jiublished descrijHioiis and figures of some palaeozoic forms, including 

 a single |>ectenoid species from the coal nieasui-es of Pennsylvania. 



In 1820, Pi-ofessor Amos Eaton notices the occuiTence of Lamellibranchiata in the New York System in 

 his " Index to the Geology of the Northern States," etc , pp. 7t)-81. No distinct species are referred to. 



In 1824, Dr. J. K. De Kay (Annals of the New York Lyceum, vol. I, p. 45, pi. 5,) published a " Note 

 im the Organic Remains, termed Bilobitbs, /»•<«« the Catskill Mountains," recognizing these fossils as prob- 

 ably the " moulds or casts of an extinct species of Cardium." These were probably the earliest notices of 

 any fossil bivalve shells from the palteozoic rocks of New York. 



