Formations in the neighbourhood of Castellane. 163 
riods of its growth. We thus see that, in certain species, the 
general form remains nearly constant, notwithstanding the in- 
crease of volume, because each new layer covers the entire 
rostrum, and is of the same thickness throughout ; while in 
other species the layers are deposited only on a part of the 
length of the rostrum, and vary among themselves in respect 
to their thickness in different parts of their extent, whence 
more or less considerable variations ensue in the exterior 
form of the shell, in proportion as the animal increases in age. 
Now, this very simple circumstance enables us to appreciate 
the influence of the progress of growth on the configuration 
of these fossil bodies, and furnishes a certain rule for distin- 
guishing the peculiarities of form inherent in the species, and 
the variations depending on the age of individuals; for each 
species carries along with it the indication of the form through 
which it has passed, and thus offers points of comparison for 
determining individuals of a less advanced age. It is in this 
way that M. Duval has been convinced that the B. linearis, 
elegans and augustus of M. Raspail, are young individuals 
of B. dilatatus of Blainville; that B. complanatus, and B. 
spathulatus of Raspail, are individuals of the same species a 
little more advanced in age ; and that B. sinuatus, ellipsoides, 
and emarginatus of the latter author, likewise pertain to this 
same species; while B. -Emerici, which may easily be con- 
founded with 2. dilatatus, and considered a variety of that 
species by M. d’Orbigny, is distinguished by its conformation 
when in a young state. 
The attentive study of the interior structure of Belemnites 
has led M. Duval to another result still more unexpected, and 
not less interesting, for it has enabled him to ascertain how 
the exterior form of these bodies may be modified in a multi- 
tude of ways more or less singular, in consequence of the frac- 
ture of the terminal portion of the rostrum, and the means of 
consolidation employed by nature to repair the injury. He 
has satisfied himself that, after such a fracture, the deposition 
of the concentric layers of the rostrum may continue to go on, 
either after the fall of the posterior fragment, or around the 
same fragment more or less thrown out of its normal position, 
and that in all the cases the shell has become deformed in a 
