The collection of Shells brought home by the United States Exploring Expe- 

 dition, on its return in 1842, was very extensive, and a large number of the species 

 were then unknown to science. Many of these latter have been since described in 

 Europe from specimens derived from other sources ; and hence can no longer be 

 claimed as additions made to science by the Expedition. 



To avoid, as much as possible, a continued subtraction from the credit of dis- 

 covery due to the Expedition, it has been determined to publish brief descriptions 

 of the new Shells, as they are prepared from time to time, in the " Proceedings 

 of the Boston Society of Natural History," from which these pages are extracted. 



In the absence of a complete library and of collections containing authentic 

 specimens, as well as from the difficulty of deciding between species and varieties 

 without the opportunity of collecting, it is too much to expect that some of the 

 descriptions may not prove to have been anticipated ; and these the writer would 

 be thankful to have pointed out. 



In the volume under preparation, more extended descriptions of the shells, 

 together with descriptions of the animals of these and of many other species, 

 will be given, and be fully illustrated by figures. 



The names to which " Couthouy MS." is appended were given by Mr. J. P. 

 Couthouy, the conchologist of the Expedition, in his manuscript notes. 



Boston, 1846. 



