X PREFACE. 



tt'.\4 and the later plates ol" this volume the author cheertiilly acknowledges the 

 very valualjle assistance rendered by Mr. Charles E. Beecher. 



Of tile mechanical and artistic execution of this work I may speak with 

 coiuniendation. Regarding the scientific character of that part of the work 

 already published and its value to the general public, we have had the testi- 

 mony of prominent scientific men ; ami I hope the present volume may be 

 reganled as an acceptable contribution tu oin- knowledge of a class of fossils of 

 which little systematic information has heretofore been given. 



The author has been indebted for the use of specimens for study and illus- 

 tration to Dr. James Knapp, of Louisville, Ky., to E. B. Knapp, Esq., of 

 Skancateles, N. Y., and to Mr. Charles E. Beecher. To the collections of the 

 Cornell University he is indebted for two specimens illustrated in the present 

 volume, and for several others which are illustrated in the plates already pre- 

 pared for the next volume. 



JAMES HALL. 



Albany, Februoni, 1884. 



