Ammonites. 
MOLLUSCA. 
21 
where they are each provided with a large, sharp, elevated 
spine, at the outer extremity of which, the ribs separate into 
three or more obtuse annulate ridges, that pass over the 
rounded back or ambit; aperture oblong, equal to nearly one- 
third of the diameter of the shell; its edge is thin and slightly 
sinuated near the inner termination. 
Discovered by Mr Murchison in the roof of the Coal at 
Brora, Sutherlandshire ; and named in honour of the noble 
family of Gower. It has also been found at Hackness and 
Scarborough, Yorkshire, in the Kelloways Rock. Professor 
Phillips mentions a variety of this species, which he has 
represented in plate 6, fig. 21, from the same localities. 
111. A. navicularis. —The Little Ship Ammonite, pi. XV. 
fig. 7. 
Ammonites navicularis. Mantell, Geology of Sussex, p. 
198, pi. 22, fig. 5. Sowerby, Min. Conch. VI. p. 105, pi. 155, 
fig. 2. De la Bechc, Geo. Manuel, p. 293. 
Umbilicate ; with from three to four narrow compressed, 
deeply inserted, rapidly enlarging, ventricose volutions; a 
numerous series of strong, smooth, elevated, annulose trans¬ 
verse ribs, emanate from the inner margin of the volutions, 
and pass continuously over the large, rounded ambit, and 
terminate on the inner margins on the opposite side of the 
volutions ; the ribs and intervening furrows are nearly of 
equal breadth ; aperture transversely oblong. Greatest dia¬ 
meter seven inches. 
Found by Gideon Mantell, Esq. in the upper Chalk at 
Offham, Sussex ; and in the lower Chalk at Guildford, accor¬ 
ding to Sowerby. 
112. A. crenularis. —The Crenulated Ammonite, pi. XV. 
lig. 8. 
Ammonites crenularis. Phillips, Geology of Yorkshire, I. 
p. 164, pi. 12, fig. 22. De la Beche, Geological Manuel, p. 
372. 
Lenticular, umbilicate ; with five moderately inflated volu¬ 
tions, the inner ones three-fourths inserted, the central three 
deeply sunk; sides crossed by strong, elevated, remote, 
somewhat curved ribs, which, on reaching the centre, are 
met by numerous smaller ribs, which pass over the sharp 
ambit, producing a crenulated subcarinated back ; aperture 
large, somewhat cordiform. 
Found in the upper Shale of the Lias formation, York¬ 
shire. 
113. A. complanatus.—T he Levelled Ammonite, pi. XV. 
fig. 9. 
Ammonites complanaius. Mantell, Geology of Sussex, p. 
118. Sowerby, Min. Conch. VI. p. 133, pi. 569, fig. L De 
la Beche, Geo. Manuel, p. 294. 
Lenticular, very flat, umbilicate ; volutions entirely con¬ 
cealed, thickest in the centre of the shell, and gradually 
contracting towards the ambit, which is protruded into a 
narrow, slightly convex, crenated carina, produced by the 
angular terminations of the plicae; inner half of the disk, with 
transverse undulating striae, and the outer portion plicated, 
extending from the back over one-third of the disk, but the 
intermediate ones only reaching about half that distance; 
aperture, slightly sagittate, not more than four-tenths of an 
inch in width ; keel with an elevation or ridge down its centre ; 
greatest thickness about an eighth of an inch ; umbilicus very 
small; septa numerous, and very foliaceous. Greatest diameter 
eight inches. 
An easily distinguished species, from its great flatness, 
extent of the outer volution, narrow keel, small umbilicus, 
and its angular plicae. 
Found in the Gray Chalk Marie, at Hamsey, Sussex, by 
Gideon Mantell, Esq. 
114. A. undatus. —The Waved Ammonite, pi. XV. fig. 10 
Ammonites undatus. Sowerby, Min. Conch. VI. p. 134, pi. 
569, fig. 2. De la Beche, Geological Manuel, p. 293. 
Discoidal, much compressed, and smooth ; with three flat 
volutions, the central ones parti}' visible, and the inner margins 
of the whole, square; ambit, slightly rounded; sides with 
remote undulations, which pass over the back; aperture, 
sagittate, greatly elongated, with obtuse angles. 
Discovered by Gideon Mantell, Esq. in the upper Chalk of 
Sussex. 
115. A. subcarinatus. —The Subcarinated Ammonite, pi 
XVI. fig. 1. 
Ammonites subcarinatus. Phillips, Geology of Yorkshire, 
I. p. 163, pi. 13, fig. 3. De la Beche, Geo. Manuel, p. 371 - 
Discoidal, lenticular, umbilicate, and subcarinate; inner 
volutions concealed ; sides slightly inflated, thick in the centre, 
and gradually sloping to the subcarinated back, or ambit; 
and crossed by numerous slightly developed ribs or undula¬ 
tions, which rise in the umbilicus, and extend to the ambit, 
crossing it, and uniting with those on the opposite side ; 
aperture nearly cordate, and equal to one-half of the diameter 
of the disk. 
The subcarina is more obvious in the inner circumference 
of the volution, and becomes gradually less distinct as it 
approaches the aperture. 
Found in the upper Shale, Yorkshire. 
116. A. laTjECOstata. — The Broad-Ribbed Ammonite, 
pi. XIV. fig. 2. 
Ammonites latcecosta. Sowerby, Min. Conch. VI. p. 106, 
pi. 556, fig. 1. De la Beche, Geological Manuel, p. 375. 
Discoidal, compressed; with five exposed flat-sided volu¬ 
tions, crossed by large, sharp, nearly parallel ribs, which 
become wider and flatter as they pass over the rounded ambit, 
where they meet and join with the ribs of the opposite side; 
all of the ribs have very indistinct indications of tubercles on 
each end ; aperture oblong. Greatest diameter three inches 
and a half. 
Found in the Lias at Lyme Regis, usually met with in the 
Alluvium. 
117. A. heteropiiy llus. — The Reversely-foliated Am¬ 
monite, pi. XVI. fig. and pi. XX. fig. II. 
Ammonites heterophyllus. Sowerby, Min. Conch. III. p. 
119, ph 266. Phillips, Geology of Yorkshire, I. p. 163, pi. 
13, fig. 2. Buckland, Geology and Mineralogy Considered, 
I. p. 347, and II. p. 59j pi. 38 and 39* De la Beche, Geo. 
Manuel, p. 37 L 
Lenticular, umbilicate; with the volutions entirely con¬ 
cealed ; sides convex, wholly covered by numerous divergent, 
elevated, slightly undulating strim; umbilicus small and 
deep; back or ambit rounded ; aperture large, occupying 
nearly two-thirds of the diameter of the disk, elliptical, with 
a slight notch for the reception of the preceding volution ; 
septa of two kinds, small, and acutely angular; and large 
and ovate; they resemble two forms of pinnated foliage ; the 
one presenting the appearance of large and oval te rminal 
leaflets; while the other is small and acutely pointed; 
siphuncle placed near the back. Greatest diameter six inches 
and three quarters. 
F 
