PREFACE.

This volume includes a report on the fossils collected during the field season of 1880 by the members of the Geological Survey of the Eureka District, transmitted for publication May 1, 1882, and additional observations and descriptions resulting from the study of collections made under the immediate direction of the writer in the summer of 1882. Eleven plates of illustration and nearly double the amount of text originally transmitted have been added, and the character of the report slightly changed. The reader will pardon the slight confusion in the arrangement of the plates resulting from this, and also the difference in the mode of illustration. The system of using wood-cuts is of great advantage, as it offers an opportunity to all for obtaining copies of the original figures by electrotyping. This is the first extended trial of the method for fine, detailed illustration, and is attempted at the special request of Major J. W. Powell, Director of the Survey.

In the preparation of the original report, frequent reference was made to the well-known Hall collection of Paleozoic fossils in the American Museum of Natural History, through the kindness of the curator in charge, Prof. R. P. Whitfield, to whom I am indebted for valuable assistance. Prof. James Hall generously gave access to the material he had accumulated for the study of the corals and lamellibranchiate shells of the Devonian, and also aided me in my comparisons between the New York and Nevada specimens. Acknowledgment is due Prof. Samuel Calvin and Dr. J. P. Farnsworth, of the State University of Iowa, for the use of specimens for comparison. The skill and care exercised by Mr. G. B. Simpson in preparing the drawings for plates ix to xx, inclusive, and by Dr. J. C. McConnell for plates i-viii, xxii-xxiv, inclusive, is shown in the plates illustrating this report.

C. D. W.

ix