8 
MOLLUSCA. 
Ammonites. 
carbonate of iron that has lined its chambers, is truly 
beautiful.” 
Our figure, pi. IV. fig. 8, is a representation of a longi¬ 
tudinal section of this species, to shew the internal structure 
of the shell, and particularly to exhibit the situation of the 
siphuncle, (preserved in a carbonaceous state,) which is seen 
passing along the whole dorsal margin, to the commencement 
of the outer chamber. The body of the animal occupied the 
space from a to b. The letters c, d , c, f (j , //, point out the 
situation of the siphuncle, which is always placed upon the 
exterior, or dorsal margin. It is represented in black, and 
passes from the external chamber i to the inner extremity of 
the volutions. 
22. A. Nutfieldknsis.—T he Nuffield Ammonite, pi. \ I. 
fig. 5. 
Sowerby, Min. Conch. II. p. 11, pi. 108. 
Involute, with four or five volutions, much concealed; 
crossed by numerous, strong, prominent ribs, with interme¬ 
diate shorter ones, which are more than three-fourths towards 
the internal side of the volutions ; these are frequently arranged 
in pairs, but the whole pass over the rounded ambit, or back; 
the larger ones being most prominent in the centre ; septa 
rather numerous, lobed and sinuated in the ordinary manner; 
aperture subcordiform, two-fifths of the diameter in length, 
nearly the same in width, and rounded behind. Diameter 
from three inches to one foot. 
This species is found abundantly in the Green Sandstone 
at Ilythe and other places, which rests above the thickest 
beds of Fuller’s Earth. Most of the specimens are casts in 
dark iron clay, and their external hue generally ochreous. 
23. A. triplicatus _Tiie Three-Pleated Ammonite, pi. 
VI. fig. 6. 
Sowerby, Min. Conch. I. p. 208, pi. 92, fig. 2. 
Involute, with four volutions, the inner ones exposed; 
surface covered with doubly curved, alternating, long and 
short ribs; between every two long ones are three short, 
which reach a little beyond the centre of the volutions ; 
septa distant; aperture obovate, about half the diameter in 
length, and its width one-third. 
In some instances there are only two intermediate ribs 
between the longer ones. 
Discovered at Portland Island by Mr Bryer of Weymouth. 
24. A. excavatus—T he Hollow Ammonite, pi. VI. fig. 7. 
Sowerby, Min. Conch. II. p. 5, pi. 105. 
Involute, lenticular, subumbilicate, with a sharp, crenulated 
carina ; on each side of which a slightly concave groove inter¬ 
venes between it and the sides of the shell, which are uniformly 
convex ; volutions about six, entirely exposed in the young 
state, and the whole divided by a flattened groove, forming 
a rectangular margin along the interior sides of the volutions ; 
the entire shell covered with obscure curved ribs, which are 
stronger in the inner volutions and in young shells ; aperture 
sagittate, extending to about half the diameter of the shell; 
and its width at back being about a third. Greatest diameter 
four inches. 
First discovered at Shotover, near Oxford, by Mr Sowerby. 
25. A. jugosus*—T he Ridged Ammonite, pi. VI. fig. 8. 
Sowerby, Min. Conch, p. 207, pi. 92, fig. 1. 
Involute, with a small, distinct, sharp carina; four volu¬ 
tions half concealed ; covered with large, obtuse, straight ribs, 
very regular, equal to the space between them, and becoming 
obsolete behind ; septa not numerous, their margins slightly 
plaited; aperture ovate, narrower behind, and occupying 
about two-fifths the diameter of the shell, and its width one- 
fifth ; shell delicate and very thin. 
Discovered by Mr Strangeways, in Limestone, at White 
Lackington Park, near Ilminster. 
26. A. communis. —The Common Ammonite, pi. VI. fig. 9. 
Sowerby, Min. Conch. II. p. 10. fig. 2, 3 ; Corne d’Amnion 
a raies doublees ver le haut du dos. Bourguet, pi. 42. 
fig. 276. 
Involute, with six or eight rounded, wholly exposed 
volutions ; crossed by numerous strong, prominent, straight 
ribs, which become furcated towards the dorsal margin, 
and are sometimes reunited on the ambit, and again divided 
on the opposite side of the shell; aperture three-fourths of 
a circle, and occupying about one-fifth the diameter of the 
shell ; septum round. 
This species is very common in the Alum Clay at Whitby; 
it is generally dark bluish-black, or brownish black, with a 
metallic lustre produced by pyrites. 
A superstitious belief prevails at Whitby, and all over the 
neighbouring country, that these Ammonites are petrified 
snakes which infested the precincts of the monastery of 
Whitby ; and these were not only turned to stone, but also 
beheaded, by a prayer from the abbess St Hilda. Indeed, 
this miracle is much insisted upon by all ancient writers who 
have occasion to mention either Whitby or St Hilda. It is 
thus alluded to by Sir Walter Scott, in Marmion ; the nuns 
are said to tell, 
And how, of thousand snakes, each one 
Was changed into a coil of stone, 
When holy Hilda pray’d ; 
Themselves, within their holy hound, 
Their stony folds had often found. 
The Convent, Stanza 13. 
There are individuals in Whitby who sell this Ammonite, 
and not unfrequently form a head upon the outer volution, 
in imitation of that of a snake, and impose upon those who 
are unacquainted with their being the remains of testaceous 
shells. 
27. A. angulatus. —The Angulated Ammonite, pi. VI. 
fig. 10. 
Sowerby, Min. Conch. II. p. 9. pi. 107. fig. 1. 
Involute, with seven or eight well rounded and wholly 
exposed volutions, which are angular along their inner sides, 
and divided by a narrow, concave, flattened space, from 
whence proceed numerous prominent ribs, which are furcated 
as they pass over the back or ambit,—which is slightly flat¬ 
tened ; aperture somewhat longer than wide, the width being 
equal to about one-fifth the diameter of the shell ; the sinu¬ 
ated margins of the septa are rather close, and considerably 
more so than in the A. communis. 
Discovered by J. M. Sowerby, Esq. in the White alum 
clay at Whitby, and has much the appearance of A. communis, 
but is at once distinguished from that species by the groove 
which separates the volutions* 
28. A. Bucklandi. —Buckland’s Ammonite, pi. VII. fig. 
1 and 2. 
Sowerby, Min. Conch. II. p. 69, pi. 130. Buckland’s Geo¬ 
logy and Mineralogy Considered, II. p. 59, pi. 37, fig. 6. 
Depressed, consisting of five volutions, the inner ones 
entirely exposed, furnished with large obtuse ribs, which 
become more produced as they approach the back, round 
