BACULITES. CEPHALOPODA. 11 
septa undulated at their margins, and the siphuncle placed 
at their outer edge. In some species, the siphuncle has a 
keel-shaped pipe raised over it; others have a series cf 
spines on each side of the ambit, or back of the shell. 
Hamites annulatus. Plate Il. fig. 4. Found in the 
Ferruginous Oolite. 
Hamites are found in the Baculite Limestone of Normandy; and a few 
small species are met with in the Chalkmarl of Folkstone. 
The most simple form of the shells of this genus may be conceived by sup- 
posing a Baculite to be curved round near its centre, until its smaller 
extremity becomes nearly parallel to its larger end. Some of the species are 
more tortuous, and are either coiled up in the form of a Spirula, or consider- 
ably less spiral. These two forms bear the same relation to Ammonites, that 
the shells of Litwola bear to Nautilus, each having a form as nearly as possible 
what these genera would respectively exhibit, if partially unrolled. 
The Hamites and Baculites possess two characters which connect them 
with the Ammonites, First, the siphuncle is situate on the ambit or outer 
margin of the shell. Secondly, the transverse plates have a foliated structure 
at their margins, where they join the external envelop or shell. In the 
Hamites, the external shell is also strengthened by transverse ribs or folds, 
which serve not only to increase the outer chambers, but also the air chambers, 
upon the same principles as in Ammonites, as we have shewn at page 14. 
There is a strong probability that the shells of this genus were partly internal 
and partly external ; those with spinous appeadages were, most likely, external 
envelops. 
The Gualt or Speeton Clay near Scarborough, Yorkshire, which occurs 
immediately under the Chalk, contains not fewer than nine species of this 
rare genus. Some of these (the Hamiles grandis in particular) are as thick 
as a man’s wrist. 
No recent species of Hamites have yet been discovered. 
Genus III. — BACULITES — Lamarck. 
Generic Character.— Shell straight, conical, symmetrical, 
cylindrical, a little compressed laterally in some instances ; 
partitions articulated by sinuous sutures ; septa close, 
transverse, and imperforate with marginal lobes and laci- 
niations ; being divided into dorsal, central, and lateral 
lobes, the external chambers larger than the rest, swelling, 
and capable of containing a considerable portion of the 
animal ; aperture elliptical, and provided with a dorsal 
siphon. 
Baculites Faujasii, Plate II, fig. 1. Found in the 
mountains of St Peter, neighbourhood of Maestricht. No 
ree species of this genus have hitherto been disco- 
vered. 
This genus may be distinguished from the Orthocera, by its septa being 
much lobed and sinuous. 
The genus Baculites takes its name from a resemblance to a straight staff. 
