PREFACE. 



When mistakes in the determination of species have 

 been ascertained, the rectifications have been given in 

 notes placed immediately beneath. The names in 

 italics indicate synonyms. 



Living ourselves amidst the scenes of the labors 

 thus recorded, we have not considered it expedient 

 to attempt an estimate of their value. Many of the 

 papers will undoubtedly require a careful revision be- 

 fore a correct opinion can be formed in this respect. 

 The arrangement of the materials, however, will, for 

 the present, enable them to speak for themselves. 



An abstract of the following pages was first pub- 

 lished in the American Journal of Science and Arts, in 

 March, of the present year. The work, as presented 

 here, is differently arranged, and embraces a larger 

 field, together with additions and improvements. 



Washington, D. C. 

 Dec. 1852. 



C. GXBARD. 



