169 
BELEMNITES. Auct. 
Gen. Cuar. An elongated, straight, ponderous, uni- 
valved, shell; cavity much shorter than the 
shell, conical, divided by septa which have 
entire even edges, and are penetrated by a 
lateral siphuncle. 
—— 
Tug shells of this long-known genus are all much elon- 
gated, never spiral nor even curved, except very slightly 
in one or two species near the apex. The chambered 
cavity is composed of thin lamine, exactly similar to the 
corresponding part in Nautilus, except that it is a 
straight, not an involute, tube or cone: this is sur- 
rounded by a coat formed of layers of fibres of a lami- 
nated or sparry structure, placed nearly perpendicularly 
to the surface, and corresponding to the outer coloured 
coat of Nautilus* or shells generally, but with the cry- 
stalline tissue much more largely developed than even 
in Pinna, with which Mr. Miller has very justly com- 
* In speaking of the various parts of a Belemnite, we shall 
keep in view this analogy: the pointed extremity will thus be 
considered as the apex, the opposite end the dase, and the side 
on which the siphuncle is placed the (as in Ammonites) front : 
we say the front, because that part of the base or aperture seems 
similarly situated to the anterior margin in the genus Helix. 
We cannot agree, when we are describing a Nautilus or Am- 
monite, to call this the back, which has often been done by other 
writers. This part in the Belemnite is by Blainville termed 
‘¢ ventrale ;’’ in Spirula the position of the siphuncle is reversed. 
