CONCH OLOGY. 
nius, who firft formed this genus in his work, dePolytha- 
lamiis, propofes nine kinds; thefe are divided into two 
feCttons, viz. ift, thofe that have the liphunculus placed 
on or near the edge ; and adly, thole that have it central, 
or near the center. It is proper to obferve, that thefe 
foflils are aim oil always calls of Hone, or replacements 
of fparry matter. For a view of the orthoceros, fee the 
Conchology-Plate II. where fig. i reprefents the recent 
fhell, cut open, to fnew the concamerations or chambers : 
this (hell is greatly'magnified; but a figure nearly of its 
natural fize is placed by its fide. Fig. z,,a fragment of 
a foflil orthoceros, fhewing its fiphunculus or pipe of 
communication, which in both thefe figures is in the cen¬ 
ter. This fragment belongs to a very large fpecies, 
though it is here Ihewn on admail fcale. 
LITUUS, the CROZIER. 
This fhell much refembles a bilhop’s crozier in fhape> 
having a long cylindric Item, one end whereof turns in a 
fpiral manner; but the fpires are few, feparated, and re¬ 
cede from each other. Breynius defcribes and figures a 
fingle fpecies, fo that it is an extremely rare foflil. But 
there is a fmall recent fhell, commonly called the ram's 
born, or nautilus fpirula of Linnaeus, found in great 
abundance both in the Ealt and Weft Indies, which is 
ranked by moPt authors as a nautilus or ammonis, and is 
the identical fpecies with the foflil kind. We only fee 
the fpiral end of this recent fhell in our collections, and 
never with its fern. However, the view alone of it 
evinces its analogy ; for as the fpires are few, and greatly 
recede from each other, it muft follow that the outer 
lpire will at laft infenfibly fall into a ftraight line or a 
item: and the reafon we never find it with the Item, pro¬ 
bably, is owing to the thinnefs and brittlenefs of the 
fhell ; fo that the agitation of the waves, for it is only 
found caft up on the {hores, eafily breaks off this ftem or 
cylindric part. Fig. 3, in the engraving, (hews the entire 
fhell; and fig. 4, is the fame cut open, to fhew its cham¬ 
bered ftruCture. 
TURBO POLYTHALAMUS, or CHAMBERED 
TURBINE. 
This genus was founded by Da Cofta. It. is only found 
foflil; and even in that ftate but one fpecies is known. 
It is a turbinated or fpiral fhell, of a produced or length¬ 
ened fhape, exactly like a buccinum in appearance, but is 
concamerated or chambered, and the diaphragms or par¬ 
titions are cut and jagged, like the foliaceous futures of 
the ammonia. Calls of ftone of this kind are found in 
Dorfetfhire, France, and §wifferland, but never in any 
great degree of perfection. Fig. 5, in the engraving 
fhews a turbo polythalamus, of the fize ufually found in 
Dorfetfhire. 
CORNUA AMMONIS, or AMMONIA. 
The fhells of this genus are perfeCl helices, the fpires 
ufually lying between two flats or levels. The fpires are 
cylindric, and connected to each other. They gradually 
diminilh or taper, on both levels equally alike, from the 
circumference to the center; fo that by the gradual ta¬ 
pering of the lpires to the center, the centers of both 
flats are concaves. The inner ftruCture is chambered 3 
but the diaphragms, or partitions of the cells or cham¬ 
bers, are notroundifh and with an even edge, as thole of 
the orthoceros and nautilus, but are llalhed, or jagged, 
into procefles or appendages, which laid together tally 
and clofe into one another fo ftrongly and curioufly, that, 
when joined, the flats or furfaces of the whole ammonis 
are embellilhed with a beautiful leaved work, exactly li- 
milarto that on the fculls of animals: and this by foflilo- 
gifts is called the foliaceous futures ot the ammonites. 
But this foliaceous work does not ieem to be a particular 
character of the ammonia, for the turbines concamerati, 
or preceding genus, have it; and there are fpecies of 0i'» 
thoceratits and fcffil nautili with the fame work. 
The fiphunculus, or pine of communication from cham- 
ber to chamber in the ammonia, feems to be placed on- 
the back of the fpires, and not near the edges, or in the 
center of them ; but, as this conclufion is drawn from 
foflil {hells, which are very rarely fo perfeCt as to (hew the 
pipe diftinCtly, we muft yet remain uncertain in regard to 
ibme of their particular characters. It is however, a 
matter of aftonilhment, that in this, and other families of 
teftacea, in general the molt common foflil (hells are the 
fcarceft in the recent ftate, and vice verfa. It could be 
readily explained, were all the foflil kinds, not known re¬ 
cent, reckoned pelagian (hells, as the ammonia certainly 
are: but then w'hat reafon can be given for the limpets, 
fea ears, volutes, cowries, &c. which, though in extreme 
plenty recent, are very rarely found foflil, with many 
other parallel inftances. The foflil ammonia, or ammo¬ 
nite, are found in great abundance, and of many fpecies, 
in mod parts of the world ; from the fmall fize of a pea* 
through all the gradations of fizes, to above a yard in di¬ 
ameter, and proportionably thick. Thefe are not objects 
that efcape the eye by their minutenefs; yet, neverthelefs, 
all the living fpecies of them (till remain to be difeover- 
ed, except one very minute kind. This living fpecies of 
ammonis is fo very minute, as hardly to exceed the big- 
nefs of a turnip feed, and does not weigh the hundredth, 
part of a grain ; therefore demands the aid of the mi- 
crofcope to examine it. It was found by Plancus with- 
the recent orthocerofes above-mentioned in the fea-fedi- 
ment at Rimini: he has deferibed and figured it in his 
work. Linnaeus ranks it among the nautiii. It is very 
remarkable, that this recent fpecies is adiftinCt kind from, 
any of the foflil ones known. It not only differs in par¬ 
ticular circumftances, but even in an efiential character 5 
which is, that as all the foflil ones, or ammonitse, have a 
concave center, this recent kind has a very prominent or 
projecting one. 
Da Cofta has fixed the fpecific characters of the foflil 
ammonitse, to be taken from the work on the back of 
their fpires ; as being the molt obvious, conftant, regular, 
and certain diftinCtion. On this character he divides the 
ammonia into eight claffes, viz. 1. Ammonia whofe 
backs are quite fmoothand plain: ammonia dorfo laevi, 2. 
Ammonia whofe backs are ftriated, fulcated, or ribbed: 
ammonia dorfo ltriato, fulcato, vel coltato. 3. Ammo¬ 
nia that have a plain prominent ridge along the back : 
ammonia limbo prominulo per totum dorfum duClo. 4. 
Ammonia with a plain prominent ridge between two fur¬ 
rows : ammonia limbo prominulo inter duos fulcos ereCto, 
5. Ammonia with a prominent ridge, nor plain, but 
wreathed or twilted like a rope : ammonia limbo tsenio- 
latu: 6. Ammonia with a plain furrow or channel along 
the back: ammonia fulco unicoper dorfum duCto. 7. 
Ammonia whofe backs ar.e ftudded or lpiked : ammonia 
dorfo tuberculato vel aculeato. 8. Ammonia whofe 
backs are deeply notched or toothed like afaw : ammonia 
dorfo dentato. Thele include all the foflil kinds hitherto 
difeovered. Fig. 6, in the copper-plate, reprefents the 
cornu ammonis, in its entire foil'll ftate, as found at Dray- 
cot, in Wiltlhire. Fig. 7, is the fame (hell, cut open to 
(hew its chambered ftruCture. 
AMMONOIDES. 
The definition of this genus is, that, in all other re- 
fpefts except (hape, it refembles the ammonitse ; for thefe 
bodies are quite globofe like nautili, and not fl.it like am¬ 
monitse. The outer fpire alone makes above one half of 
the body ; and all the other fpiies are very fmall, and ta¬ 
per into a concavity, fo that the center is deeply hollow¬ 
ed or umbilicated. Linnaeus dalles thefe among his nau¬ 
tili. Thefe elegant foflils are found with the preceding, 
at Draycot in Wiltfhire, and in Swiflerland. Fig. 8, in 
the engraving, is an exaCt delineation of this curious (hell. 
The NAUTILUS. 
The nautili are defined to be (hells, whofe fpires never 
appear 
