68 
explanation of plate 44 '. 
chambered alveolus in the Belemnite, (Fig. 7. b. h'.) 
but has no Siphon. (Blainville.) 
Fig. 4'. Longitudinal section of the apex of the shell of 
Sepia officinalis. This apex is composed of granular 
calcareous matter (a.)^ alternating with conical horny 
laminte, which expand laterally into the horny mar- 
gin (e.). (Original.) 
Fig. 5. Longitudinal view of Fig. 4. The apex (a.) re- 
presents the apex of a Belemnite. The back of the 
shell (e.) the dorsal part of a Belemnite ; and the 
alveolar portion (Z>. b' .) represents the internal cham- 
bered shell of a Belemnite. (Blainville.) 
Fig. 6. Anterior extremity of the lamellse, or alveolar 
plates, exposed by a longitudinal section in Fig. 5. 
In the mature animal these lamellae are nearly 100 
in number ; a few of them only are here I’epresented. 
These alveolar plates form the internal chambers 
of the Sepiostaire, and represent the transverse 
plates of the Alveolus in Belemnites, and other 
chambered shells; but as the Sepiostaire has no 
siphuncle, its chambers seem not subservient, like 
those of the Belemnite, to the purpose of varying 
the specific gravity of the animal ; the intervals be- 
tween its plates are occupied by an infinite number 
of thin winding partitions standing perpendicularly 
between the lamellae. 
Figs. 6'. 6". Thin calcareous partitions winding between, 
and supporting the alveolar plates of the Sepiostaire. 
The sinuous disposition of these partitions increases 
their efficacy in resisting pressure, on the same 
principle, as in the foliated edges of the transverse 
plates of Ammonites.* The sinuosity of the cal- 
* Dr. Fleming lias accurately described the structure of these 
partitions, as exhibiting perpendicular laminae, waved and folded in 
brain-like gyrations which occasionally anastomose. 
