Ammonites. 
MOLLUSCA. 
15 
66. A. perarmatus. —The Well-armed Ammonite, pi. XI. 
fig. 2. 
Ammonites perarmatus . Sowerby, Min. Conch, p. 7*2, 
pi. 352. 
Discoidal, compressed; four exposed volutions, armed with 
two concentric series of acute tubercles; these are transversely 
united by eighteen or twenty pairs of obtuse ribs upon each 
volution ; the remaining portion of the shell is plain and 
flat; ambit rounded; aperture longer than wide, almost 
orbicular, and occupying in length about one-third of the 
diameter of the disk. Greatest diameter eight and a half 
inches. 
Found in the Coral Rag at Malt on, in the Coral Oolite, 
Calcareous Grit, and Kelloway’s Rock, Yorkshire. 
67. A. Smitiii. —Smith’s Ammonite, pi. XI. figs. 4, 5. 
Ammonites Smitki. Sowerby, Min. Conch. IV. p. 148, 
pi. 406, figs. 1, 2, 3, 4. 
Discoidal, compressed, carinated ; five nearly wholly ex¬ 
posed volutions, crossed by many slightly curved distant 
ribs; sides flattened ; keel obtuse ; aperture oblong-ovate. 
Greatest diameter two inches. 
The surface of this species exhibits a beautiful pearlaceous 
lustre. It is subject to great variety in its aspect from the 
young to the adult state. In its very young stages, it is 
nearly globose, entirely plain, and umbilicate, as in fig. 3; as 
it increases in growth, its ribs are gradually developed, first 
in the form of somewhat elongated tubercles, near the margin 
of the umbilicus ; soon after this, the keel appears, and it 
then approaches its mature state, with the flattened shape 
and fully formed ribs, as in fig. 4. 
Found associated with Ammonitesplanicosta, pi. VII. fig. 7, 
in the dark Marly Limestone, called Marston Stone, at 
Marston Magna, near Ilohester, and also at Evershot, Somer¬ 
setshire. It bears some resemblance to that species, but is at 
once distinguished by the ribs being destitute of the tubercu* 
lated sharpness of that shell. 
Named in honour of W. Smith, Esq. an excellent geologist, 
and author of a Geological Map of England, &c. 
68. A. fibulatus. — The Button and Loop Ammonite, 
pi. XI. fig. 5. 
Ammonites armatus . Young and Bird, Geology of York¬ 
shire, p. 250, pi. 13, fig. 9. A. jibulatus. Sowerby, Min. 
Conch. IV. p. 147, pi. 407, fig. 2. 
Discoidal, much compressed ; six volutions, the inner ones 
almost entirely exposed, flattened on their sides, with their 
inner margins plain; traversed by numerous transverse ribs, 
which are joined in pairs by smooth spines; these increase 
the uncommon flatness of this species, by filling up at inter¬ 
vals the suture which separates the volutions ; there are 
placed at unequal distances ribs which pass over the dorsal 
margin without uniting with the spines; these are more 
numerous in the external volutions, and in some instances, 
alternate with the spines; each rib, when disengaged from 
the spine, is distinctly separated into two, consequently a 
greater number of costas pass over the back than are found 
upon the sides of the shell ; aperture oblong. It is distin¬ 
guished from Ammonites armatus, pi. VIII. fig. 2, by its 
smooth spines. 
Found in the Lias, at Whitby, &c. Yorkshire. 
69. A. subarmatus. — The Subarmed Ammonite, pi. XI. 
fig. 1. 
Ammonites subarmatus . Young and Bird, Geology of 
Yorkshire, p. 250, pi. 13, fig. 3; Sowerby, Min. Conch. IV. 
p. 146, pi. 407, fig. 1. 
Discoidal, compressed, concave ; six volutions, the inner 
ones almost entirely exposed ; sides crossed by slightly curved 
ribs, which are frequently united in pairs by smooth spines 
at their exterior extremities, continuing to nearly the central 
volution, but on the outer volutions these generally disap¬ 
pear; and the ribs, which, in the earlier volutions, are usually 
divided before they pass over the back, arc but seldom split. 
The spines are hollow, the sides of the volutions are 
convex and increase rather rapidly in size, but are, like 
the Ammonites mutabiles , pi. XIII. fig. 7, a little constricted 
in some places. 
Found in the Lias, at Whitby, Yorkshire. 
70. A. Dayvei. —Davy’s Ammonite, pi. XI. fig. 7. 
Ammonites Davcei. — Sowerby, Min. Conch. IV. p. 70, 
pi. 350. 
Discoidal, compressed; about five entirely exposed volu¬ 
tions, their sides almost flat, with very numerous transverse, 
slightly arcuated ribs, the interstices between them being 
nearly equal to their breadth, with a series of remote obtuse 
tubercles in the centre of the volutions, each covering about 
four of the sulci ; aperture nearly orbicular. Found in the 
Blue Lias at Lyme Regis, Dorsetshire. 
Named in honour of the distinguished Sir Humphrey Davy. 
71. A. LiEviGATUS—The Smooth Ammonite, pi. XI. fig. 8. 
Ammonites lawigatus. Sowerby, Min. Conch. VI. p. 135, 
pi. 570, fig. 3. 
Discoidal, compressed, smooth ; three convex volutions, 
the inner ones exposed ; aperture transversely oblong-ovate, 
with a thickened margin, somewhat produced in front. 
Found in the Lias, at Lyme- Regis. 
72. A. parvus —The Small Ammonite, pi. XI. fig. 9. 
Ammonites parvus. Sowerby, Min. Conch. V. p. 70, pi. 
449, fig. 2. 
Discoidal; four or five* gradually enlarging volutions, the 
inner ones exposed; sides furnished with numerous, elevated, 
obtuse, divergent, undulating striae ; ambit considerably 
rounded ; aperture ovate, occupying one-third of the diameter 
of the disk. 
Discovered in the shaft, while sinking a well at Tunbridge, 
eighty feet below the surface. 
73. A. cri status.—T he Cristed Ammonite, pi. XI. fig. 10. 
Ammonites cristatus . Defrance, MSS.; Sowerby, Min. 
Conch. V. p. 24, pi. 421, fig. 3. 
Lenticular, compressed, carinated ; inner volutions con¬ 
cealed, the outer one increasing rapidly; keel thin, largely 
and deeply notched. 
Found at Weymouth by Mr Bryer. 
74. A. Bakeri.e. — Baker’s Ammonite, pi. XI. fig. 11, 
and 14. 
Ammonites BakerUe. Sowerby, Min. Conch. VI. p. 134, 
pi. 570, figs. 1, 2. 
Discoidal, compressed; four volutions, inner ones exposed ; 
sides with transverse, numerous, furcated, armed ribs, and 
about ten or eleven sinuous lines,—which are its distinguishing 
characteristic,—extending over the back; aperture oblong- 
ovate. 
Discovered by Miss Baker in an indurated nodule of 
Marie amongst Alluvium, parish of Braunston, Northamp¬ 
tonshire, and named in honour of that lady. 
75. A. Herveyi. —Hervey’s Ammonite, pi. XI. fig. 12. 
