.MAKYLAND GKULOUICAL SUKVEY 17 



the small size of the collections of Eocene specimens found in the various 

 museums of the country, as compared with the collections of Neocene 

 forms from the same area. The forms figured and described in this 

 report have come, with scarcely an exception, from the collections of the 

 United States National Museum, tiie Academy of iSFatural ' Sciences of 

 Philadelpliia, the Johns Hopkins University, and the Maryland Geo- 

 logical Survey. The Museum of the Academy of Natural Sciences of 

 Philadelphia contains Dr. Conrad's types, which have been most im- 

 portant in definitely determining the species hitherto described. 



The State Geological Survey desires to express its thanks for the aid 

 which has been rendered by the several experts who have contributed to 

 this volume; also to the U. S. Geological Survey which has generously 

 allowed the use of many of its plates and drawings, whicli have materially 

 reduced the expenses of publication; and to Professor G. D, Harris for 

 the loan of several drawings. 



Many important suggestions have also been received from Dr. W. H. 

 Dall of the U. S. Geological Survey, Professor H. A. Pilsbry of the 

 Philadelphia Academy of Natural Sciences and Mr. C. W. Johnson of 

 the Wagner Free Institute of Science. They have examined many of 

 the determinations of fossils, and have thus materially contributed to 

 the accuracy of the report. 



Thanks are also due to the artists Mr. J. C. McConnell of the U. S. 

 Army-Medical Museum, Mr. H. C. Hunter of the U. S. Geological Sur- 

 vey and Mr. F. von Iterson for the beautiful drawings with which the 

 report is illustrated. 



