Ammonites. 
MOLLUSCA. 
23 
Ammonites plicatilis. Sovverby, Min. Conch. II. p. 149, 
pi. 16G. Fleming, Brit. An. p. 242. De la Beclie, Geo. 
Manuel, p. 370. 
Discoidal, with six exposed volutions ; sides flat, crossed 
by numerous, equal, straight ribs, which become bifurcate 
or trifurcate towards the rounded ambit, which is smooth in 
the centre ; aperture quadrangular, with rounded angles, a 
little longer than wide ; septa acutely sinuated. Thickness 
of the shell about one-fourth its diameter. 
So straight, close, and uniform are the ribs of this species, 
that they have more the appearance of art than of nature; in 
some cases, they are simple ; in others, bifid or trifid. 
Found in the Sandy Limestone of Dry Sandford and 
Marsham, north west of Abingdon ; in the Kelloways Rock, 
Coral and Oolite, Yorkshire; the Coral Rag, middle and 
south of England ; and in the same kinds of strata in various 
places on the Continent. 
124. A. Jamesoni.—J ameson’s Ammonite, pi. XVI. fig. 10. 
Ammonites Jumesoni. Sovverby Min. Conch. VI. p. 105. 
pi. 555, fig. 1. Phillips, Geology of Yorkshire, I. p. 163. 
De la Beche, Geo. Manuel, p. 372. 
Discoidal; with five or six volutions, the inner ones ex¬ 
posed ; crossed by large, simple, obtuse, slightly bent ribs, 
which curve forward as they pass over the rounded ambit, 
meeting those on the opposite side, and are nearly equal to 
the intermediate spaces ; aperture oblong-ovate, its length 
being equal to twice its breadth. 
Discovered in the Lias, Island of Mull, by R. I. Murchison, 
Esq. and named by him in honour of Professor Jameson of 
Edinburgh ; it has also been found in the Lias of Yorkshire, 
at Robin Hood’s Ba} r . 
125. A. Johnstoni. —Johnston’s Ammonite, pi. XVII. 
fig. i. 
Ammonites Johnstoni . Sovverby, Min. Conch. V. p. 70. 
pi. 449, fig- 1- Fleming, Brit. An. p. 247- De la Beche, 
Geo. Manuel, p. 375. 
Discoidal, with from six to nine greatly compressed, 
one-third inserted volutions; crossed by a central series 
of numerous, short, straight, elevated ribs, or perhaps more 
properly, elongated tubercles ; inside of the volutions and 
ambit plain ; central volutions destitute of ribs, and of nearly 
equal thickness. 
When its outer coating is removed, this species exhibits 
the most brilliant play of iridescent colouration. 
Discovered in the Lias Clay at Watchet, Somersetshire, 
by Mr Johnstone, and named by Sovverby in honour of him ; 
and has since been met with in the Lias at Bath. 
126. A rotiformts. — The Wheel-Shaped Ammonite, pi. 
XVII. fig. 2. 
Ammonites rotiformis . Sovverby, Min. Conch. V. p. 76, 
pi. 453. Fleming, Brit. An. p. 247- De la Beche, Geo. 
Manuel, p. 375. 
Depressed, carinated ; sides somewhat concave, with from 
six to eight entirely exposed volutions ; crossed by numerous, 
distant, strong, slightly bent [elevated ribs, each provided 
with an oblong, obtuse tubercle at its outer extremity ; ambit 
flat; keel slightly sunk, and with a furrow on both sides ; 
aperture almost square, a little longer than wide, and only 
one-sixth the diameter of the shell. Greatest diameter seven 
inches. 
Found at Yeovil in the Lias, and also in the Lias at 
Bath. 
127- A.bifrons.—T he Two-Fronted Ammonite, pi. XVII. 
fig. 3. 
Ammonites bifrons. Phillips, Geology of Yorkshire, I. p. 
141, pi. 6, fig. 18. De la Beche, Geo. Manuel, p. 37 L 
Discoidal, subumbilicate ; with three or four moderately 
convex, rapidly increasing volutions, the inner ones one-third 
concealed ; a series of remote, rounded, prominent, and nearly 
straight ribs, emanate from the inner margin of the volutions ; 
and after reaching two-thirds across the sides, terminate, and 
are met by numerous smaller ribs, which pass over the 
rounded ambit, producing a crenulated profile. 
Found in the Kelloways Rock at Hackness, in Yorkshire. 
128. A. longispinus.—T he Long-Spined Ammonite, pi. 
XVII. fig. 4. 
Ammonites longispinus. Sovverby, Min. Conch. V. p. 164, 
pi. 501, fig. 2. Fleming, Brit. An. p. 247- 
Discoidal, thick; with three or four plain, half inserted 
volutions ; sides furnished with two concentric series of spini- 
form tubercles ; ambit thick, smooth, and gently rounded ; 
aperture orbicular, deeply indented by the contiguous volu¬ 
tion ; its greatest diameter somewhat more than three-fifths 
of the diameter of the disk ; external surface pearlaceous. 
Found near Weymouth, Dorsetshire. 
129- A. contractus. — The Contracted Ammonite, pi. 
XVII. fig. 5. 
Ammonites contractus. —Sovverby, Min. Conch. V. p. 162, 
pi. 500, fig. 2. De la Beche, Geo. Manuel, p. 373. 
Subglobose, deeply umbilicate; inner volutions nearly 
concealed ; sides contracted, appearing as if drawn into the 
umbilicus, around which are a series of large rather acute 
tubercles, from which emanate numerous smooth rounded 
ribs, these branch into sets of three or four, and pass over 
the greatly rounded back or ambit, and join those on the 
opposite side ; aperture oblong, arcuated. 
Found in the Inferior Oolite at Dundry ; and in the same 
strata, Normandy. 
130. A. Turneri —Turner’s Ammonite, pi. XVII. fig. 6. 
Ammonites Turneri. Sovverby, Min. Conch. V. p. 75, pi. 
452. Fleming, Brit. An. p.244. De la Beche, Geo. Manuel, 
p. 372. Phillips, Geology of Yorkshire, I. p. 164, pi. 14, 
fig. 14 ? 
Depressed, carinated ; with five volutions, the inner ones 
almost entirely exposed ; sides flattened, with numerous equal 
ribs, which continue almost straight until reaching nearly the 
back, where they are suddenly curved forward ; carina but 
moderately elevated, with a furrow on each side; aperture 
oblong, quadrangular, its length being about one-third the 
diameter of the disk. 
This shell is not unlike Ammonites J3rooJtie y pi. XI. fig. 13, 
but is distinguished by its more exposed volutions, in the 
somewhat square aperture, and in the different curvature of 
the ribs. 
Found in the Lias at Watchet, Wymondham Abbey, and 
in the lower Shale of the Lias formation, Robin Hood’s Bay, 
Yorkshire. 
131. A. ljevi use ulus.— The Smoothish Ammonite, pi. 
XVII. fig. 7- 
A?nmonites Iceviusculus. Sovverby, Min. Conch. V. p. 73, 
pi. 451, fig. 1, 2. Fleming, Brit. An. p. 244. De la Beche, 
Geo. Manuel, p. 373. 
Discoidal, carinated, umbilicate; with four or five rapidly 
increasing volutions, the inner ones being partly exposed 
