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- 
* Mr. Conrad had already, in 1835, published descriptions and figures of some palaeozoic forms, including 
a single pectenoid species from the coal measures of Pennsylvania. 
In 1820, Professor Amos Eaton notices the occurrence of Lamellibranchiata in the New York System in 
his “ Index to the Geology of the Northern States,” etc , pp. 76-81. No distinct species are referred to. 
In 1824, Dr. J. E. De Kay (Annals of the New York Lyceum, vol. I, p. 45, pi. 5,) published a “ Note 
on the Organic Remains, termed Bilobites, from 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 palaeozoic rocks of New York. 
