PREFACE. 



This volume contains the descriptions and illustrations of the Trilobites 

 and other Crustacea of the Oriskany, Upper Helderberg, Hamilton, Port- 

 age, Chemung and Catskill groups of the New York Geological Series, which 

 essentially constitute the equivalent of the Devonian System of Europe. 

 Some descriptive matter and illustrations, supplementary to Volume V, part ii, 

 are also included. 



The volume, as it will now go to the public, is very different in its scope and 

 character from the original conception and plan of the author. 



While still free to devise a scheme for the completion of the Palaeontology 

 of New York, in what appeared to him the most satisfactory manner, he had 

 contemplated a review and revision of all his previous work upon the Pal.eozoic 

 Crustacea, the early part of which had been done with very incomplete and 

 often unsatisfactory material and equally imperfect knowledge of the subject. 

 With this end in view, an effort was made, in 1873, through private subscription 

 of the citizens of Albany, to purchase from Mr. C. D. Walcott a collection of Tren- 

 ton limestone fossils, mainly for the sake of the Trilobites which it contained. 

 This plan failing, the collection went to the Museum of Comparative Zoology, 

 in Cambridge. At a later period, a second similar collection was offered to the 

 State Museum by Mr. Walcott, but its purchase was not effected. This collec- 

 tion like the preceding one was purchased by the Museum in Cambridge, which 

 now possesses a series of New York Trenton limestone fossils far superior to 

 any other in the country. 



In the meantime the author had, at his own personal expense, sent an assist- 

 ant into the field to make collections, especially of Trilobites, from the rocks 



