BELEMISITE COMPARED WITH NAUTILUS. 377 
Comparing the shell of Belemnite, with that 
of Nautilus, we find the agreement of all their 
the absence of the nacreous horny sheath, by supposing that a 
condition of the matrix favourable to the preservation of the 
calcareous sheath was unfavourable to the preservation of horny 
membrane ; and we may also explain the absence of ink-bags, 
by supposing that the decomposition of the soft parts of the 
animal usually caused the ink to be dispersed, before the body 
was buried in the earthy sediment then going on. 
At the base of Golden Cap hill, near Charmouth, the shore 
presents two strata of marl almost paved with Belemnites, and 
separated by about three feet only of comparatively barren marl. 
As great numbers of these Belemnites have Serpuloe, and other 
extraneous shells attached to them, we learn from this circum- 
stance that the bodies and ink-bags had decomposed, and the 
Belemnites lain some time uncovered at the bottom. These 
facts are explained by supposing that the sea near the spot was 
much frequented by Belemno-sepise during the intervals of the 
deposition of the Lias. Similar conclusions follow, from the 
state of many Belemnites in the chalk of Antrim, which had 
been perforated by small boring animals, whilst they lay at the 
bottom of the sea, and these perforations filled with casts of 
chalk or flint, when the matter of the chalk strata was deposited 
upon them, in a soft and fluid state. (See Allan's Paper on 
Belemnite, Trans. Royal Soc, Edin., and Miller's Paper, Geol. 
Trans. Lond. 1826, p. 53.) 
Thus of the millions of Belemnites which crowd the Secondary 
formations, only the fibro-calcareous sheath and chambered al- 
veoli are usually preserved ; whilst in certain shale beds this 
sheath and shell have sometimes entirely disappeared, and the 
horny or nacreous sheath and ink-bag alone remain. See PI. 44'', 
Fig. 1,2, 3, 4, 5, 6, 7, 8. In the rare case, PI. 44', Fig. 7, 
which has afforded the clue to this hitherto unexplained enigma, 
we have all the three essential parts of a Belemnite preserved in 
their respective places nearly entire. The ink-bag (c) is placed 
within the anterior horny cup (e, e', e") ; and the chambered 
alveolus (b b') within the hollow cone of the posterior fibro- 
calcareous shell, or common Belemnite. 
