REPORT ON THE DEPARTMENT OF MOLLUSKS (INCLUDING CENOZOIC IN- 

 VERTEBRATE FOSSILS) IN THE U. S, NATIONAL MUSEUM, 1887. 



By W. H. Dall, Honorary Curator. 



The force of the Department of Mollusks beside the curator has con- 

 sisted of Dr. E. E. C. Stearns, adjunct curator ; Miss Agnes Nicholson, 

 clerk (to February, 1887); Mr. Pierre Louis Jouy, aid (since February, 

 1887). 



Assistance has also been rendered from time to time, by permission 

 of the Director of the U. S. Geological Survey, by Messrs. E. Stuart, 

 Frank Burns, and E. T. Hill, of the Geological Survey, chiefly in con- 

 nection with the Tertiary fossils contributed by the Survey to the 

 Museum. 



The work, as during the past years, has chiefly consisted in the clas- 

 sification and preparation of material received during the year and left 

 over from previous years. By the faithfulness and industry of those 

 employed upon the work, good progress has been made, and with sim- 

 ilar success during the next two or three years we may hope to see the 

 last of eleven years' arrearages (to 1884) finally administered upon. 



This once accomplished it will be a comparatively easy task to keep 

 up with the annual accessions except in very unusual cases. 



As there is no logical or biological reason for separating the Tertiary 

 fossils from the recent shells in general administration (though the 

 specimens may be kept in separate cases for convenience of reference), 

 no separation has been made, and this report therefore is practically a 

 report on the Department of Tertiary Invertebrate Fossils as well as of 

 the Department of Mollusks. 



A biological arrangement has been adopted in arranging the fossils, 

 the distinctions of supposed age being retained only on the labels. 

 The result of this is to bring together all the species of any one genus 

 from the Eocene to the Post Pliocene, and, in the writer's opinion, a 

 study of the collection thus arranged is likely to reduce by two-thirds 

 the number of nominal species now on our lists of Tertiary fossils of 

 the United States. 



The general collection is divided into three principal geographical 

 series with two subordinate groups, all being biologically arranged. 

 Thus we have the species of West America from the Arctic province 



ill 



