IV 



In the investigation of fossil eelrinoids, I was so fortunate as to 

 secure the assistance of S. A. Miller, Esq., of Cincinnati, whose 

 familiarity with that class of organism renders his determinations 

 of more than ordinary value, and his work has resulted in the 

 satisfactory elucidation of some very difficult and rather unsatisfac- 

 tory material. 



The illustrations for this volume were mostly drawn by Mr. 

 Charles K. Worthen, and are faithful reproductions of the original 

 specimens ; and the plates have been engraved and printed by 

 Messrs. Julius Mayer & Co., of Boston, in their usual excellent 

 style. 



One hundred and sixty-five plates of fossils have been published 

 in the preceding volumes of the Geological Survey of Illinois, which, 

 with those contained in the present volume, brings the aggregate 

 number now published up to one hundred and ninety-six, nearly all 

 of which have been devoted to the illustration of species new to 

 science, and mainly obtained in prosecuting the field work of the 

 geological survey, from formations existing within the borders of the 

 State. 



The work, however, is by no means complete, and at least two 

 volumes more, illustrated by forty to fifty plates each, would be re- 

 quired to complete the palaeontology of the State in the manner 

 originally contemplated. These volumes should also include such 

 economical results as may be obtained in the meantime by future 

 investigations. 



Nothing further can be done in this direction, however, until pro- 

 vision is made for it by a special act of the General Assembly, and 

 it remains for the legislative authorities to determine whether the 

 work shall be continued and eventually completed, in accordance 

 with the original plan, or cease with the publication of the present 



volume. 



A. H. WORTHEN. 



