362 SPIRULA. 
of a Cephalopod. We further learn, from Peron's 
discovery of the shell of a Spirula partially en- 
closed within the body of a Sepia,* (see PL 44, 
Fig. 1, 2), that many of those genera of fossil 
chambered shells, which, like the Spirula, do 
not terminate externally in a wide chamber, 
were probably internal, or partially enclosed 
shells, serving the office of a float, constructed 
on the same principles as the float of the Spi- 
rula. In the class of fossil shells thus illustrated 
by the discovery of the animal inclosing the 
Spirula, we may include the following extinct 
families, occurring in various positions from the 
earliest Transition strata to the most recent 
Secondary formations ; — Orthoceratite, Lituite, 
Baculite, Hamite, Scaphite, Turrilite, Nummu- 
lite, Belemnite.t 
* The uncertainty which has arisen respecting the animal 
which constructs the Spirula, from the circumstance of the spe- 
cimen discovered by Peron having been lost, is in some degree 
removed by Captain King's discovery of another of these shells, 
attached to a fragment of the mantle of an animal of unknown 
species resembling a Sepia, which I have seen in the possession 
of Mr. Owen, at the Royal College of Surgeons, London. 
t In the genus Lituite, Orthoceratite, and Belemnite, PI. 44, 
J. 3, 4, 17, the simple curvature of the transverse plates resem- 
bles the character of the Nautilus. In the Baculite, Ham.ite, 
Scaphite, and Turrilite, PI. 44, Fig. 5, 8, 12, 13, 14, 15, the 
sinuous foldings and foliated edges of the transverse plates 
resemble those of the Ammonites. 
