INK BAG. 375 
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, 
altered by pressure. It is composed of a thin laminated sub- 
stance (see PI. 44", Fig. 1, d.), which in some parts is brilliantly 
nacreous, whilst in other parts it presents simply the appear- 
ance of horn. The outer surface of this cup is marked trans- 
versely with gentle undulations, which probably indicate stages 
of growth. Miss Baker has a Belemnite 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. Pom- 
pilius. 
M. Blainville, although he had not seen a specimen of Belem- 
nite 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 sound- 
ness of his reasoning is confirmed by the discovery of the speci- 
men before us, containing this part in the form and place which 
he had predicted. " Par analogic elle etait done evidemment 
dorsale et terminale, et lorsqu'elle etait complete, c'est-a-dire 
pourvue d'une cavite, I'extremite posterieure des visceres de 
I'animal (tres-probablement I'organe secreteur de la generation 
et partie du foie) y etait renfermee." — Blainville Mem. sur les 
Belemnites. 1827. Page 28. 
Count Munster (Mem. Geol. par A. Boue, 1832, V. 1, PI. 4, 
Figs. 1,2, 3, 15) has published figures of very perfect Belemnites 
from Solenhofen, in some of which the anterior horny sheath is 
preserved, to a distance equal to the length of the solid calcareous 
portion of the Belemnite (PI. 44', Figs. 10, 11, 12, 13), but in 
neither of these are there any traces of an ink-bag. 
