Ammonites. 
MOLLUSCA. 
27 
flat, crossed by many broad, flat, waved ribs ; which, after 
passing the centre, sweep elegantly forward ; ambit thin ; 
aperture somewhat sagittate. 
Found in the upper Shale at Boulby, Yorkshire. 
159. A. rostratus. — The Beaked Ammonite, pi. XIX. 
fig. 10. 
Ammonites rostratus, Sowerby, Min. Conch. II. p. 16.3, pi. 
172 ; Fleming, Brit. An. p. 245 ; De la Beche, Geo. Manuel, 
p. 294. 
Compressed, carinated, with about four wholly exposed, 
flattened volutions ; their sides crossed by large, strong, 
remote, slightly bent ribs, each of which is provided with 
three or four oblong tubercles ; larger on the extremity of 
the ribs next the ambit, over which they project; aperture, 
elliptical, somewhat less than one-third the diameter of the 
disk, and, at the ambit, terminating in a slightly reflected and 
compressed beak, which is almost closed. The tubercles arc 
somewhat confluent on the outer volutions, but are more dis¬ 
tinctly divided, and developed on the inner volutions. Great¬ 
est diameter seven inches and a quarter. 
Found in Chalk Marie, Rock’s Village, near Benson, 
Oxfordshire, and in the Sussex Chalk. 
160. A. Henleyji. — Henley’s Ammonite, pi. XIX. 
fig. 11. 
Ammonites Henleyii. Sowerby, Min. Conch. II. p. 161, pi. 
172.; Fleming’s Brit. An. p. 245 ; De la Beche, Geo. Manuel, 
p. 371. 
Discoidal, with three or four wholly exposed, rapidly 
increasing volutions ; sides crossed by many flattened ribs, 
which emanate from the inner sides of the volutions, curving: 
slightly from the aperture, and after reaching the centre one, 
provided with large compressed tubercles, from whence they 
become bifurcate, the branches gently curving backwards, 
and, after passing over the ambit, unite on the opposite side, 
producing a crenulated margin to the back, when viewed 
in profile ; the ribs are also furnished with a tubercle, a little 
way from their origin ; between this and the central row, the 
volutions are a little concave ; aperture nearly orbicular, 
being two-fifths the diameter of the disk, with a small sinus, 
produced by the preceding volution ; greatest diameter six 
inches. 
Found in the Lias at Lyme Regis, Dorsetshire ; and also 
that of Yorkshire, and the middle and south of England. 
161. A. baltiatus. — The Belted Ammonite, pi. XX. 
fig. i. 
Ammonites baltiatus. Phillips, Geology of Yorkshire, I. 
p. 163, pi. 12, fig. 17; De la Beche, Geo. Manuel, p. 372. 
Discoidal; volutions entirely exposed ; crossed by nume¬ 
rous, strong, elevated ribs, which emanate on the inner mar¬ 
gins of the volutions, and pass over the rounded ambit, every 
alternate rib being somewhat less elevated on the back. 
Found in the Lias, Yorkshire. 
162. A. decipiens. — The Deceitful Ammonite, pi. XX. 
figs. 2 and 9. 
Ammonites decipiens. Sowerby, Min. Conch. III. p. 169, 
pi. 294, fig. 1 and 2 ; Fleming, Brit. An. p. 243 ; De la 
Beche, Geo. Manuel, p. 374. 
Discoidal, thick ; with five or six exposed volutions, crossed 
by large, elevated ribs, which rise a little way from the inner 
margin, and, crossing the sides, become obscure towards the 
ambit, which is rounded ; aperture oblong. 
This shell presents a very different appearance in the adult 
and young conditions. In the latter state, when the large ribs 
have passed the centre of the sides, they are met by nume¬ 
rous small ribs, which are entirely wanting in the adult 
shell. 
hound in Clay at Highgate Ilill, and at Pakefield, near 
Lowestoft, Suffolk. 
163. A. ovatus. —The Ovate Ammonite, pi. XX. fig. 3. 
Ammonites ovatus. Phillips, Geology of Yorkshire, 1. p. 
164, pi. 13, fig. 10 ; De la Beche, Geo. Manuel, p. 373. 
Lenticular, umbilicate ; the inner volutions entirely con¬ 
cealed, their margins alone being visible within the small 
and deep umbilicus ; sides thick internally, and sloping 
towards the back, which is thin and slightly flattened, crossed 
by numerous, undulating, depressed ribs, which emanate at 
the internal margin, and after passing the centre, bend 
sweepingly forward. 
Found in the Hard Bands, in the Lias formation at Ilaw- 
sker, Yorkshire. 
164. A. venustus. — The Graceful Ammonite, pi. XX. 
fig. 4. 
Ammonites venustus. Phillips, Geology of Yorkshire, I. 
p. 122, pi. 2, fig. 48 ; De la Beche, Geo. Manuel, p. 294. 
Discoidal, thick, with three or four rapidly increasing 
volutions, the inner ones half concealed ; sides crossed by 
many straight, elevated ribs, equal to the interstices between 
them ; which, on reaching the centre, are met by numerous, 
strong, rounded, gently curved ribs, which pass over the 
ambit, and meet with those on the opposite side, producing 
a crcnated margin at the back; aperture oblong. 
Found in the Speeton Clay, at Speeton, Yorkshire. 
165. A. concinnus. — The Comely Ammonite, pi. XX. 
fig. 5. 
Ammonites concinnus. Phillips, Geology of Yorkshire, 
I. p. 123. pi. 2. fig. 47. De la Beche, Geo. Manuel, 
p. 294. 
Discoidal, thick, with four rapidly increasing volutions, 
the inner ones half inserted; a series of strong remote ribs 
emanate from the inner margins of the volutions, bending 
slightly forward, and are met in the centre by numerous, 
acute, elevated ribs, which pass over the rounded ambit, and 
meet with those on the opposite side ; aperture roundish. 
Found in the Speeton Clay, at Speeton, Yorkshire. 
166. A. Minimus. — The Smallest Ammonite, pi. XX. 
fig. 6. 
Ammonites , “ like A. parvus .” Phillips, Geology of 
Yorkshire, I. p. 187, pi. 2, fig. 46. 
Discoidal, thick, witli three volutions, the inner ones two- 
thirds inserted, and the outer ones increasing rapidly ; sides 
crossed by numerous, curved ribs which rise on the inner 
margins, and pass over the rounded ambit, meeting those of 
the opposite side; aperture oblong. 
Found in the Speeton Clay, Yorkshire. 
167. A. cuuviNoiDEs. — The Curved-Ribbed Ammonite, 
pi. XX. fig. 7 . 
Ammonites curvmoides. Phillips, Geology of Yorkshire, I. 
p. 123, pi. 2. fig. 50; De la Beche, Geo. Manuel, p. 294 . 
Volutions, flattened with remote, elevated, waved ribs, 
which emanate from the inner edges of the volutions, and as 
they approach the ambit are suddenly and acutely curved 
towards the aperture; between these are several depressed 
and nearly obsolete ribs ; ambit rather thin. 
Found in the Speeton Clay, Yorkshire. 
