MOLLUSCA. 
342 
fissure ; from the exterior surface being marked with a longitudinal gutter on one side, or with two or 
several gutters towards the summit ; or as that surface is smooth and without gutters. 
Some fossils, very much like the Belemnites, hut without a cavity, and even with a protruding basis, 
form the genus Actinocamax of Miller. 
It is upon similar conjectures that the classification of the 
Ammonites, Drug., or Snake-stones,— 
Is founded, for they, also, are only found in a fossil state. They are distinguished, in general, from 
Nautilus, by their septa, which, instead of being plain or simply concave, are angulated, sometimes 
undulated, but oftener gashed on the margins, 
like the leaves of the Acanthus. The smallness 
of their last cell leads to the belief that, like the 
Spirula, they were internal shells. The beds of 
the secondary mountains swarm with them, and 
we find them there from the size of a bean 
to that of a chariot wheel. The variations 
of their whorls and of their syphon enable 
them to be subdivided. Thus the name 
Ammonites, Lam., is restricted to the species in which all the whorls are visible. Their syphon 
is near the margin. They have been still further distinguished into those which have the margins 
of the septa foiiaceous, (the Ammonites, the Planites of Haan,) and into those in which they 
are simply angular and undulatory (the Ceratites of Haan). Those in which the last whorl envelopes 
all the others, are the Orhulites, Lam., or the Glohites and Goniatites of Haan, or Peloguses, Montf. 
The syphon is the same as in Ammonites.* The name Scaphites, Sowerby, [or rather of Parkinson,] 
has been appropriated to those species whose whorls are contiguous and on the same plane, excepting 
the last, which is detached and bent upon itself. Those which are perfectly straight are the Baculites, 
Lam. Some are round, others are compressed ; and in the latter we some- 
times observe the syphon to he lateral. The Hamites of Sowerby, [Par- 
kinson,] are known by having their first formed cells arcuated. But the 
Turrilites, Montf., differ more than any from the usual habit of the family, 
for the whorls, in place of remaining on the same level, descend rapidly, 
and give to the shell that obelisk form which is denominated turriculated. iss.— Portion of a Bacuiite 
From analogy, it is supposed that we ought to refer to the Cephalopods, and to consider as being in- 
ternal shells 
Fig. 154. — Ammonites 
The Camerines, Brug. {Nummulites, Lam.), — 
For all of them are equally fossil. They have a lenticular shape, without any apparent aperture, but 
within there is a spiral cavity, divided by septa into a multitude of little chambers without a syphon. 
They are amongst the most generally diffused fossils, and almost of themselves form some entire chains 
of calcareous hills, and immense banks of building stone. (It is upon such rocks that the pyramids of 
Egypt are founded, and with stones of the same description that they are built.) 
The commonest, and which attains the largest size, are altogether discoid, and have only a single 
row of chambers in the whorl of the spire. Some minute sorts of this description have been also found 
recent in some seas. Other minute species, both living and fossil, have their margin bristled with points, 
which give to them the figure of stars {Siderolithes, Lam.). 
The works and the patient researches undertaken successively hy Bimchi {or Janus Plancus), Soldani, 
Fichtel and Moll, and Alex. d’Orbigny, have made known an astonishing number of these chambered 
and esyphonal shells {Nummularia), of extreme littleness, so as often to be altogether microscopical, 
either in the sea, among sand, sea-weed, &c. ; or, in a fossil state, in the sand-beds of various countries ; 
and these shells vary to a remarkable extent in their contour, the number and the relative position of 
their chambers, &c. One or two species, the only ones in which the animals have been noticed, have, 
apparently, a small oblong body surmounted by numerous red tentacula, a structure which, taken in 
* According to Sowerby, Orbulites and Ammonoceras, of Lamarck, are not distinct from Ammonites. The Ammonocetas is only an acci- 
dentally worn portion of an Ammonite. — E d. 
