PLATE XI. 
1. Ammonites Peramplus. ( Very large Ammonite.) Discoidal; witli four or five ventricose volutions, 
inner ones nearly half-inserted, outer one increasing rapidly in dimensions, occupying one-third diameter 
of disk; sides, with a few distant, obtuse ribs, most conspicuous on inner sides of volutions, and obsolete 
before reaching rounded, plain ambit; aperture transversely obovate ; septa crisped, sinuated. 
2. A. Perarmatus. {Well-armed Ammonite .) Discoidal, compressed; with four exposed volutions, 
armed with two concentric series of acute tubercles, transversely united by eighteen or twenty pairs of 
obtuse ribs on each volution; rest of shell plain, flat; ambit rounded; aperture longer than wide, almost 
orbicular. Greatest diameter, 8£ in. 
3. 4. A. Smithi. {Smith's Ammonite.) Discoidal, compressed, carinated; with five nearly wholly 
exposed volutions, crossed by many curved, distant ribs; sides flattened; keel obtuse; aperture oblong- 
ovate. Greatest diameter, 2 in. 
5. A. Fibulatus. {Button and Loop Ammonite.) Discoidal, compressed; with six volutions, inner ones 
almost entirely exposed, flattened on sides, with inner margins plain, crossed by many transverse ribs, 
joined in pairs by smooth spines; ribs at unequal distances passing over dorsal margin without uniting 
the spines; these latter more numerous in external volutions, and sometimes alternate with spines; each 
rib, when separate from spine, divided into two; hence more costae pass over the back than are found upon 
sides of shell ; aperture oblong. 
6. A. Subarmatus. {Sub-armed Ammonite.) Discoidal, compressed, concave; with six volutions, inner 
ones almost entirely exposed; sides, crossed by slightly curved ribs, frequently united in pairs by smooth 
spines at exterior extremities; ribs on outer volution seldom divided. Spines hollow; sides of volutions 
convex, increasing rapidly in size. 
7. A. Dayaei. {Day's Ammonite.) Discoidal, compressed; with about five entirely exposed volutions ; 
sides flat, with numerous transverse arcuated ribs, with a series of remote, obtuse tubercles in centre of 
volutions ; aperture nearly orbicular. 
8. A. Laevigatus. {Smooth Ammonite.) Discoidal, compressed, smooth; with three convex volutions, 
inner ones exposed; aperture transversely oblong-ovate, with thickened margin. 
9. A. Parvus, {Small Ammonite.) Discoidal ; with four or five volutions, inner ones exposed ; sides, 
with numerous elevated, obtuse, divergent, undulating striae ; ambit considerably rounded ; aperture ovate, 
occupying one-third of diameter of disk. 
10. A. Cristatus. {Crested Ammonite.) Lenticular, compressed, carinated; inner volutions concealed, 
outer one increasing rapidly ; keel thin, deeply notched. 
11. 14. A. Bakeriae. (Baker's Ammonite.) Discoidal, compressed; with four volutions, inner ones ex¬ 
posed ; sides, with transverse, many furcated, armed ribs, and about ten or eleven sinuous lines extending 
over back ; aperture oblong-ovate. 
12. A. Herveyi. {Hervey's Ammonite.) Discoidal, gibbous, umbilicate; with four volutions, inner ones 
nearly concealed; sides, with many arcuated, sharp, bifurcate, or trifurcate ribs; umbilicus very deep, with 
sides smooth, quadrangular; aperture semi-lunar, with obtuse angles; thickness of shell nearly equal to half 
diameter. Greatest diameter, 54 in. 
13. A. Brooki. {Brook's Ammonite.) Discoidal, compressed, carinated; with four or five volutions, inner 
ones not quite half concealed; sides, with many strong, simple, arcuated ribs; also marked by fine lines 
of growth; keel round, entire, with deep sulcus on each side ; aperture oblong-ovate; about one-third of 
diameter of shell. Greatest diameter, 6£ in. 
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