jt- PREFACE. 



to indicate a considerahle nuinhcM- of new generic forms, which it is believed are 

 well founded in nature, and which will prove useful in the study of this class 

 of fossils. The totiU number of genera described in the volume is sixty-five, 

 of which twenty-six are new to science. Thirteen of these belong to the 

 Monomyaria and thirteen to the Dimyaria. 



The total number of species described is five hundred and twenty (520), of 

 which two hundred and thirty-eight (238) belong to the division Monomyaria, 

 and two hundred and eighty-two (282) to the Dimyaria. Four hundred and 

 eighty-five (485) of these species belong to the Devonian System, as at present 

 recognized. Thirty-five are from the Waverly or Lower Carboniferous, and 

 five Silurian species are introduced for the piu*pose of comparison. The 

 former volumes of the Palaeontology contain altogether descriptions and illus- 

 trations of about twenty genera and one hundred species of Lamellibranchiata. 



In the revision of the species, and the publication of this volume, the author 

 acknowledges with great satisfaction the assistance rendered by Mr. C. E. 

 Beecher. The original drawings of the fossils have been chiefly made by 

 Mr. George B. Simpson. About twelve plates are by Mr. Emerton, and four 

 by Mr. J. W. Hall ; the supervision of the drawing and lithography was in 

 charge of Mr. R. P. Whitfield. The six plates of recent additions have been 

 drawn by Mr. E. Emmons. The lithography has been done chiefly by Mr. 

 Philip Ast and Mr. Paul liiemann. 



The author has been indebted for the use of specimens for illustration in 

 this volume to the late Dr. James Knapp, of Louisville, Kentucky ; to Prof. 

 J. S. Newberry and Prof. J. J. Stevenson, of New York ; to Mr. C. E. Beecher, 

 of Albany, and for the loan of specimens from the collections of the Cornell 

 University. Prof. Winchell, of Ann Arbor, has kindly loaned the types of all 

 his described species from the Marshall Group and Burlington sandstones, of 

 which farther use would have been made in comparisons with New York 

 forms, but for the fact that he intends soon to publish the descriptions of the 

 same with full illustrations of the species. 



Albany, November, 1885. 



