The fact of these animals having been provided with so
large a reservoir of ink, affords an à priori probability that
they had no external shell; the ink-bag, as far as we yet
know, being a provision confined to naked Cephalopods,
which have not that protection from an external shell,
which is afforded by the shell of the N. Pompilius to its
inhabitant, that has no ink-bag. No ink, or ink-bags have
been ever seen within the shell of any fossil Nautilus or
Ammonite: had such a substance existed in the body of the
animals that occupied their outer chamber, some traces of
it must have remained in those beds of lias at Lyme Regis,
which are loaded with Nautili and Ammonites, and have
preserved the ink of naked Cephalopods in so perfect a condition.
The young Sepia officinalis, whilst included within
the transparent egg, exhibits its link-bag distended with ink,
provided beforehand for use as soon as it is excluded; and
this ink-bag is surrounded by a covering of brilliant nacreous
nite from the inferior Oolite near Northampton, in which one half of the fibrous cup being removed, the structure of the conical shell of the alveolus
is seen impressed on a cast of iron-stone, and exhibits undulating lines of growth, like those on the exterior of the shell of N. Pompilius.
M. Blainville, although he had not seen a specimen of Belemnite in which the anterior horny conical chamber is preserved, has argued from the analogy of other cognate chambered shells that such an appendage was appertinent to this shell. The soundness of his reasoning is confirmed by the discovery of the specimen before us, containing this part in the form and place which he had predicted. 'Par analogie elle était donc évidemment dorsale et terminale, et lorsqu'elle était complèt c'est-à-dire pourvue d'une cavité, l'extremite postérieure dee viscères de l'animal (très-probablement l'organe sécréteur de la generation et partie du foie) y était renfermée."—Blainville Mem. sur les Bèlemnites. 1827. Page 28.
Count Munster (Mem. Geol. par A. Boue, 1832, V, 1, Pl. 4, Figs. 1, 8, 3, 15) has published figures of very perfect Belemnites from Solenhofen, in some of which the interior horny sheath is preserved, to a distance equal to the length of the solid calcareous portion of the Belenmite (Pl. 44', Figs. 10, 11, 12, 13,) but in neither of these are there any traces of an ink-bag.
