REPORT OF THE SECRETARY. 21 



its introduction, the time when it appears to have attained its maxi- 

 mum development, and that at which it is supposed to have died out, 

 if not represented in our existing seas. At the head of each generic 

 description the etymology of the name and the type of the genus, 

 when known, are given. Full descriptions of each of the families 

 including these genera are likewise given ; and at the end of each 

 family description the names of all the genera, whether living or ex- 

 tinct. The introduction contains detailed descriptions of the various 

 formations in which these fossils existed, with remarks on their 

 synchronism with other American and European deposits. 



A considerable portion of the specimens described and figured were 

 collected by Dr. F. V. Hayden in the several expeditions into the 

 regions of the Upper Missouri and Yellowstone, sent by the govern- 

 ment under the command of Lieutenant (now Major General) G-. K. 

 "Warren, of the United States Topographical Engineers, to whose 

 scientific zeal and liberal encouragement Ave are indebted for much of 

 the material upon which the work is fotmded. But besides these, a 

 large number were collected by Dr. Hayden himself previous to his 

 connexion with the exploring expeditions of the government. The 

 specific descriptions of the fossils described in this work are therefore 

 to be regarded as appearing, in the joint names of Meek and Hayden, 

 while the descriptions of the genera, and families, and the discussion 

 of their relations, geological range, geographical distribution, &c., 

 are to be accredited to Mr. Meek alone. 



The first sketch of this work was prepared as a part of the report 

 to Congress of the explorations of the above-mentioned regions, but 

 Mr. Meek has since devoted almost three years exclusively to extend- 

 ing and completing the investigations; and as it is probable that Con- 

 gress will make no provision for its publication, it has been adopted 

 by the Institution, at the earnest recommendation of several eminent 

 naturp^lists, and will be published in successive parts. All the speci- 

 mens described are in the collections of the Institution, and as soon 

 as the work is completed the numerous duplicates will be distributed, 

 as types of the species, to various scientific institutions at home and 

 abroad. 



3Iiscellaneous Collections. — Several series of articles forming parts of 

 the Miscellaneous Collections, as stated in previous reports, have been 

 undertaken, of which some have been completed, some are still in 

 hand, and others have been printed during the past year. 



The first of these series is that relating to the shells of North 

 America, and will consist of the following works : 



