xu INTRODUCTION. 



tions, within the same area, is more than six hundred (600), of which about 

 five hundred (500) are from the rocks above the Oriskany sandstone. 



In 1842, Mr. Connvd having resigned his position as PaliBontologist of the 

 Survey, without making any final Report, the Geologists were left to their own 

 resources in providing illustrations of the characteristic fossils of the forma- 

 tions within their several districts. The final Reports of the State Geologists, 

 therefore, will be found to contain illustrations of a considerable number of 

 the Lamelli branch lata. 



During the interval named, and for many years subsequently, the writer, both 

 personally and by the aid of his assistants, made extensive collections of this 

 class of fossils in the State of New York, and to a less extent in other States. 



At a still later period, from 1856 to 1870, extensive collections were made 

 preparatory for the Palaeontology of the State, through the means afforded by 

 appropriations of money by the Legislature. 



In making preliminary studies of these fossils, the author found that the 

 types of Mr. Conrad's species were to a great .extent inaccessible, or were dis- 

 tributed through the collections of several institutions, and of private individuals. 

 In order to secure accuracy in the identification of the described forms, he 

 availed himself of the assistance of Mr. Connid for the study and comparison 

 of all the species. On three several occasions Mr. Conrad spent a considerable 

 time in Albany, in the study of the collections here accumulated ; and in the 

 identification and determination of species, labeling one or more specimens of 

 tho.se which he recognized as typical forms of the species he had previously 

 described. In this manner, and by later studies and comparisons, it is believed 

 that proper identification has been made with nearly all the described forms, 

 and due credit has been given in this wotk. 



From the time Mr. Conrad ceased his publications upon the Lamellibriinchiata, 

 numerous writers have published descriptions and illustrations of American 

 species of this class of fossils, until at the present time the entire number of 

 palaeozoic species recorded is more than twelve hundred and fifty. 



The principal authors, who have contributed to our knowledge of the subject, 

 are given below in alphabetical order. To cite the date and title of the pub- 



