2 TRANS. OF THE WAGNER FREE INSTITUTE, PHILADELPHIA. 



with the progress in systematic classification of the recent fauna, which bears 

 equally upon the extinct forms when they are perfectly recognized. 



The present paper, it is hoped, will make a beginning in the direction of a 

 better and more natural classification of our Tertiary moUusks and of a 

 clearance of the ground of synonyms, erroneous identifications and other 

 misconceptions. It is, of course, not to be expected that the work can be 

 fully carried out e.xcept by the combined efforts of all our paleontologists and 

 the expenditure of years of labor and scientific devotion. By using a biologic 

 instead of a stratigraphic system of division for the animals studied, the 

 relation of the different faunas at once takes on an absorbing interest. I 

 believe that the practice common in museums of arranging the fauna of each 

 horizon only in a series of drawers by itself, is responsible for much retarda- 

 tion in paleontologic science. The ideal museum should have two series, one 

 stratigraphic and one biologic, and in the latter should be arranged together 

 all the animals of one family from its earliest to its latest appearance. In the 

 present state of science, if but one system can be adopted, I believe that the 

 biological sequence is by far the most important, notwithstanding some obvious 

 inconveniences which attend it. 



To the institutions above mentioned and to the officers of the Academy of 

 Natural Sciences, Philadelphia, the members of the U. S. Geological Survey, 

 and especially to Mr. Joseph Willcox, Mr. James Shepard, of New Britain, 

 Connecticut ; Mr. F. W. Crosby, of Washington, and various friends and 

 correspondents in Florida, my thanks are due for co-operation and assistance. 



The types of the fossils described are deposited in the Museum of the 

 Wagner Free Institute of Science and the U. S. National Museum. The 

 Museum of the Philadelphia Academy of Natural Sciences and the U. S. 

 National Museum contain most of the original types of Conrad and other early 

 paleontologists, and with them, when any question arose, the specimens here 

 described have been carefully compared. 



The drawings which have been photographically engraved for the illustra- 

 tions of this paper were drawn with the pen by Dr. J. C. McConnell, of 

 Washington, and Mr. J. H. Ridgway, of the U. S. Geological Survey. All 

 those representing small species were outlined by camera. I think that 

 these illustrations speak with sufficient clearness for themselves. 



