INTRODUCTION. 



In drawing up the descriptions, I have endeavoured to use language 

 as simple and definite as possible, and, by comparing each species with 

 the one most nearly allied to it, to make its peculiar character appa- 

 rent. Where a shell bore characters somewhat prominent, I have 

 endeavoured to select a specific name significant of them, almost en- 

 tirely avoiding local and complimentary appellations. I have retained 

 names selected by Mr. Couthouy, unless they had been preoccupied ; 

 and, where his descriptions have mainly been used, his initials are 

 appended ; the revision of them, and the determination that they did 

 not relate to shells already described, having been made by myself. 



After the most scrupulous endeavours to avoid describing shells 

 which had been previously named, consulting all the books and the 

 best collections in the country, with this view, it is quite likely that 

 the evil has not been entirely avoided. The history of a contem- 

 poraneous Voyage of Exploration in nearly the same track, has been 

 in the course of publication simultaneously ; and, from a recent exa- 

 mination of a few of the plates of the Voyage of the Astrolabe and 

 Zele*e, several species appear to be there figured, which are also de- 

 scribed in this work. It is believed, however, that the descriptions 

 published in the Proceedings of the Boston Society of Natural History 

 were of prior date, and must, therefore, be adopted. 



The formation of new genera from characters of the shell alone, has 

 been avoided. In some few instances, where new forms of mollusks 

 have been presented, such as could not be united with received genera 

 without violence, a new genus has been instituted. In instances where 

 generic divisions seemed justifiable, I have rested contented with in- 

 dicating groups, without formally establishing them. In several cases 

 it has been possible to present, for the first time, or essentially to cor- 

 rect, the characters of the mollusk, thus contributing something 

 towards a natural classification. 



In this collection of descriptions of new species, where so many 

 genera do not appear at all, and very few are fairly represented, no 

 accurate systematic arrangement could be expected, and none has been 

 attempted. 



