viii PREFACE. 



Duriiij^ and since this period the writer has made extensive collections of 

 these fossils, hoth with his own hands and through the agency of his assistants, 

 preparatory for their illustration in the Palaeontology of New York. After 

 having accumulated considerable collections, and feeling the importance of their 

 proper identification, tlic writer per.sonally engaged Mr. Conrad to examine the 

 whole and to give his determination of the species which he had described. On 

 three several occasions, previous to 18G5, Mr. Conrad visited Albany for the 

 express purpose of making these determinations and identifications, labelling one 

 or more of each of those which he recognized as typical forms of the species. 

 Through these means and by later study and comparison it is believed that 

 nearly all the previously described forms have been satisfactorily determined. 



The species described in this volume are illustrated from original drawings 

 made from typical or authenticated specimens. These specimens are chiefly 

 selected from the State Museum collections, which were derived from the 

 State Geological Survey, from subsequent acquisition by purchase, or from field 

 collections especially made for this object. 



The work of lithographing the plates of the Lamellibranchiata was begun in 

 1870, and owing to the author's constant occupation in duties pertaining to the 

 State Museum, the supervision of the drawings and lithogra^jhy were chiefly 

 intrusted to Mr. R. P. Whitfield, who at that time was acting as draughtsman 

 and museum assistant, and the first thirty plates of this volume were drawn, 

 and lithographed, and arranged under his direction. 



Unfortunately the species had not, at that time, been critically studied, and 

 in a final revision at a later period (1880) it became necessary to make an 

 arrangement of the genera and species which is not in accordanci" witli the 

 arrangement upon these plates. In the course of the work it has been Ibuiid 

 necessary to reproduce, in a more correct form, with illustration of tlie parts, 

 some of the figures of the earlier i^lates, as well as to give many additional species. 

 All these later illustrations are given on Plates Ixxxi-xcii inclusive, which are 

 arranged in systematic order, with the generic forms in their natural relation 

 to each othci-. It is to be regretted that these plates cannot be arranged in 

 consecutive order with those preceding, but in the earlier part of the work the 



