X 
PREFACE. 
All the later drawings have been made by Mr. E. Emmons. Many of the 
plates which bear the name of Mr. George B. Simpson, were drawn between 
1870 and 1881, and have remained in the hands of the author awaiting 
publication. 
The accuracy and completeness of the original drawings will be acknowledged 
both by the author and by the student in this department of Palaeontology. 
Much the larger proportion of the lithography has been done by Mr. Philip 
Ast, the completion of some of the plates bearing his name dating back to 1872. 
In the continuation of the work, since 1886, Mr. Paul Riemann has done a 
smaller number of the plates. In consequence of the pressure for the comple¬ 
tion of the work within a specified time, the standard of quality originally 
established has not been maintained in this and the preceding volume, but the 
deterioration has principally come through the printing of the plates. 
The typographical and mechanical execution of the work speaks for itself. 
March, 1888. 
THE AUTHOR. 
