vill PND RiO DD UIC TON: 
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 
Zelée, several species appear to be there figured, which are also de- 
seribed 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. 
