THE SESSILE BARNACLES (CIRRIPEDIA) CONTAINED IN 

 THE COLLECTIONS OF THE U. S. NATIONAL MUSEUM; 

 INCLUDING A MONOGRAPH OF THE AMERICAN 

 SPECIES. 



By HENRY A. PILSBRY, 



Special Curator of the Department of Mollusca, Academy of Natural Sciences of 



Philadelphia. 



INTRODUCTION. 



This work is a continuation of the author's report on the Cirripedia 

 contained in the United States National Museum, of which the por- 

 tion relating to pedunculate forms was published in 1907. It was at 

 first intended to record the species of sessile Cirripedia in the Museum, 

 with their localities, and to describe and figure new forms. As the 

 collection was worked over, its wealth in American barnacles became 

 apparent. It contains nearly every known species of the Western 

 Hemisphere, many of them in hundreds, even thousands, of individ- 

 uals, often showing aspects of variation special to American waters. 

 This has led to an alteration hi the scope of the work, which may be 

 described as a monograph on American sessile barnacles, with the 

 records of foreign species contained in the Museum interpolated in 

 sj^tematic order. In cases where extended investigation of Old 

 World barnacles has been essential to a right appreciation of our 

 own, the results have been included herein. It is behoved that these 

 interpolations will not seriously detract from the use of the work for 

 the determination of American species, while it is an advantage to 

 have all the information relating to a given species or genus in one 

 place. 



The deep-water barnacles of our coast are nearly all new to science, 

 but a majority of the American littoral species have been described 

 in Darwin's monograph. 1 His grasp of detail was so comprehensive 

 and his language so lucid that one can not expect to improve upon 

 them. In the field he covered one can not do better than to imitate. 

 Yet it has been possible to extend the work in certain directions. 

 By the use of higher powers than were commonly used upon such 

 objects 60 years ago, important features, unknown to Darwin, are 

 found in the cirri. Various reforms in classification have been under- 



1 A Monograph on the Subclass Cirripedia, the Balauidse, the Verrucidae. London, 1854. 



