CHAMBERED ALVEOLUii. 
373 
distance. PI. 44', Fig. 7, b, e, e', e". This horny 
cup formed the anterior chamber of the Belem- 
^^ite, and contained the ink bag, (c), and some 
other viscera.* 
Thirdly, a thin conical internal chambered 
shell, called the Alveolus, placed within the cal- 
careous hollow cone above described. (PI. 44, 
l^ig. 17, a. and PI. 44', Fig. 7, b, b'.) 
This chambered portion of the shell is closely 
allied in form, and in the principles of its con- 
struction, both to the Nautilus and Orthoceratite. 
(See PI. 44, Fig. 17, a, b. and Fig. 4.) It is 
divided by thin transverse plates into a series 
of narrow air-chambers, or areolce, resembling 
a pile of watch-glasses, gradually diminishing 
towards the apex. The transverse plates are 
outwardly concave, inwardly convex ; and are 
perforated by a continuous siphuncle, (PI. 44, 
h'ig. 17, b.), placed on the inferior, or ventral 
Uiargin. 
We have already (Ch. XV. Section II.) des- 
cribed the horny pens and ink-bags of the Loligo, 
found in the Lias at Lyme Regis. Similar ink- 
hags have recently been found in connection 
with Belemnites in the same Lias. Some of these 
hik-bags are nearly a foot in length, and show 
this lamiaated honiy sheath is rarely preserved in coiinec- 
*-'on with the fibro-calcareous shelly sheath ; but in the Lias at 
hyrae Regis it is frequently found without the shell. Certain 
I^Uions of it are often highly nacreous, whilst other parts of the 
sheath retain their horny condition. 
