1V PRELIMINARY REMARKS. 
Gould’s Report under the same names, and yet the changes 
made are only such as the present state of the science demands, 
and as result from examinations of the animal in species in 
which it was before unknown. Since attention has been di- 
rected to the subject, the researches of zoologists on the coasts 
of Greenland, Norway, Sweden, Denmark, Great Britain, and 
Sicily, —as Moller, Sars, Lovén, Forbes, Clark, Alder, Phi- 
lippi, and others, — have made us acquainted with the mollus- 
cous animals of those countries, some of which are identical 
with those of our own. I have myself made descriptions and 
figures of nearly all the species found on the New England 
coast, which I shall take some other opportunity to publish. 
The number of species now added to the number described 
in Dr. Gould’s work is eighty-four. 
For the arrangement of the Gasteropoda, I have adopted, 
with a few trifling modifications, that of Professor Forbes and 
Mr. Hanley, in the “ British Mollusca and their Shells,” a mag- 
nificent and extended work which has been in the course of 
publication during the last four years. In some points I should 
have preferred to deviate from this classification, but as we 
must still remain far from the truth, in a class in which the true 
relations of the groups are so little known, I have used the ap- 
proved mode as most convenient and conducive to uniformity, 
until more certain data are derived from Embryology and 
Homology. 
In the classification of the Acephala, it will be seen that I 
have reversed the usual order, and made other modifications 
of the established arrangement. For explanations of my views 
