MOLLUSCA. 
Ammonites. 
6 
principal folds; aperture approaching to six-sided, equal to 
about two-fifths of the diameter, and one side embracing the 
adjoining volution ; septa numerous and very foliaceous. 
First discovered by G. A. Mantell, Esq. at Itingmer, east 
of Lewes, Sussex. 
Mr Mantell says, “ The number and disposition of the ribs 
and tubercles of this species are so various, that although it 
is one of the most abundaut productions of the Gray Marie, 
its specific characters are not easily defined. 
The general form of the shell is discoidal, the volutions 
(which, when perfect, arc nearly cylindrical) being flattened 
by compression, as in the specimens figured by Mr Sowerby. 
The inner wreaths in those which are compressed are nearly 
two-thirds concealed, but in more perfect examples are less 
deeply inserted. The costae are round, and extend alter¬ 
nately across the whorls, the intermediate ones embracing 
about two-thirds of the volutions. The tubercles constitute 
the following varieties: — 
u Variety 1. costata .—With two rows of tubercles, tablet 
21 , fig. 9* Two tubercles are placed on every rib, and form 
a row on each margin of the ambit or back of the shell. This 
is a beautiful cast, from Middleham. The specimen, fig. 1 , 
tablet *22, also belongs to this variety. It exhibits the folia¬ 
ceous septa, and the situation of the siphunculus. It was 
collected by my friend, Thomas Woolgar, Esq. of Lewes.” 
We have represented this variety on pi. IV. figs. 4 and 9. 
“ Variety 2 . tuberculo-costata *—With six rows of tubercles. 
This variety, in addition to the marginal tubercles, has four 
rows, which are placed on the lower costa; only, each side of 
the shell having one set on the margin of the umbilicus, and 
another at a short distance above it. 
Variety 3. tubcrculata . — With eight rows of tubercles. 
The two additional sets which distinguish this variety are 
placed on each side, midway between the margin of the 
ambit and the second row of tubercles from the umbilicus. 
These intermediate tubercles occur on every rib, each of the 
larger costa? being ornamented with eight, while the shorter 
ones have but four. From the numerous tubercular projec¬ 
tions on this variety, the outer volution is somewhat penta¬ 
gonal. 
The septa of Ammonites Mantelli are numerous, and very 
foliaceous. The form of the aperture varies in different 
specimens, but its width is in general equal to about two- 
fifths of the diameter of the shell. The siphunculus is small, 
and extends along the centre of the ambit. 
This species frequently attains a large size, exceeding one 
foot and a half in diameter, but in these the tubercles are 
nearly obliterated.” 
Mantell’s Ammonite has been found in almost every spot 
in Sussex where an excavation has been made in the Gray 
Marie. 
7* A. costatus. —The Ribbed Ammonite, pi. V. fig. 2. 
With four depressed volutions ; margin three-sided, broad, 
and flattened ; volutions about two-thirds concealed, with 
strong radiating ribs, some of which, in the inner volutions, 
do not reach entirely across ; sides somewhat flattened ; aper¬ 
ture six-sided ; ambit trigonal. 
From the Limestone at Uingmer, Sussex. 
This species is nearly allied to Ammonites Mantelli , and is 
probably only a variety of that shell. 
8 . A. mi nut us—The Minute Ammonite, pi. IV. fig. 10. 
Sowerby, Min. Conch. I. p. 116, pi. 53. fig. 3. 
Orbicular, with a small umbilicus, thickness and diameter 
nearly equal; inner volutions concealed, with numerous con¬ 
centric, wide stria?, about twenty-four in number; aperture 
semilunar; from two to three lines in diameter. 
Found at Folkstone, Kent, by Mr Gibbs. 
9. A. Lam bert i—Lambert’s Ammonite, pi. V. fig. 1. 
Sowerby, Min. Conch. III. p. 73, pi. 242, figs. 1, 2, and 3. 
Discoid, depressed, numerously radiated, curved over 
the back ; alternately long and short, but rarely furcated ; 
the longer radii are strong, and emanate from the inner 
margin of each volution, curving forward when past the 
centre, at which place they sometimes branch, but generally 
from this situation the shorter ridges take their rise, and 
proceed to the edge, producing an imperfectly crenulated, 
sharp carina; aperture lanceolate. Diameter about four 
times its thickness ; greatest diameter two inches and a half. 
In some individuals the radii are considerably more pro¬ 
duced than in others, especially in the last volution of the 
larger ones, where t hey become proportionally less numerous. 
Found at Weymouth, Portland Island, and Sandfoot 
Castle. 
10. A. acutos. —The Acute Ammonite, pi. V. fig. 3. 
Sowerby, Min. Conch. J. p. 51, pi. 17, fig. 1. 
Somewhat depressed, with three or four volutions, the 
inner ones half exposed; surface provided with slightly 
bent ribs, which gradually thicken as they diverge from the 
inner margin, where they commence, and terminate a little 
way beyond the centre of the volutions; slightly carinated, 
with the margin crenulated and flattish ; aperture somewhat 
cordiform, and two-fifths the diameter of the shell. Diameter 
an inch and three-eighths ; thickness three-eighths. 
Found in the Cliff, near Minster, Isle of Shepey, and in 
Portland Island, and the London Clay. 
11 . A. omphaloides. — The Umbilicated Ammonite, pi. 
V. fig. 4. 
Sowerby, Min. Conch. III. p. 74, pi. 242, fig. 5. 
Gibbous, inner volutions half concealed, the outer ones 
increasing rapidly; with produced, waved ribs, bending 
forward in the centre of the back, and several of which are 
furcated, but not always united to the larger ones; back 
broad and rounded ; aperture transversely oblong, occupying 
more than half of the diameter of the shell. 
Found near Weymouth, and in Portland Island. 
Sowerby says the ribs sometimes unite to two alternate 
ones on opposite sides of the volutions, forming a zig-zag line 
upon the back. 
12. A. uuadratus. — The Square-mouthed Ammonite, 
pi. V. fig. 5. 
Sowerby, Min. Conch. I. p. 52, pi. 17, fig* 3. 
Somewhat depressed, with four or five volutions, the inner 
ones half concealed ; surface covered with produced, undu¬ 
lating, nearly uniformly thick, furcated ribs, extending into 
the carinated and crenatcd margin, which is not flattened, 
with irregular intermediate shorter ribs hardly reaching 
the centre ; aperture somewhat quadrangular, extending to 
about a third of the diameter of the shell. Diameter an inch 
and five-eighths ; thickness half an inch. 
Found in a gravel pit at Brandstone, near Framlingham, 
Suffolk. 
13. A. giganteus. —The Gigantic Ammonite, pi. V. fig. 6. 
De Montfort, p. 92 ; Lister, pi. 1046 ; Sowerby, Min. 
Conch. II. p. 55, pi. 126. 
