PLATE V. 
1. Ammonites Lamberti. {Lambert's Ammonite.) Discoidal, depressed, numerously radiated; 
alternately long and short, rarely furcated; aperture lanceolate; diameter about four times its 
thickness. Greatest diameter, 2f in. 
2. A. Costatus. {Ribbed Ammonite.) With four depressed volutions; margin three-sided, 
broad, flattened; volutions about two-thirds concealed, with strong, radiating ribs; sides somewhat 
flattened; aperture six-sided; ambit trigonal. 
3. A. Acutus. {Acute Ammonite.) Somewhat depressed, with three or four volutions, inner 
one half exposed; surface, with slightly bent ribs; slightly carinated, with margin crenulated, 
flattish; aperture somewhat cordiform and two-fifths diameter of shell. Diameter, If in.; thick¬ 
ness, f in. 
4. A. Omphaloides. {Umbilicated Ammonite.) Gibbous, inner volutions half concealed, outer 
ones increasing rapidly; with produced, waved ribs; back broad, rounded; aperture transversely 
oblong, occupying more than half diameter of shell. 
5. A. QuadratUS. {Square-mouthed Ammonite.) Somewhat depressed; with four or five 
volutions, inner ones half concealed; surface, with produced, undulating, nearly uniformly thick, 
furcated ribs; aperture somewhat quadrangular, extending to about a third of diameter of shell. 
Diameter, If in.; thickness, f in. 
6. A. Giganteus. {Gigantic Ammonite.) Depressed, with usually six volutions; surface with 
numerous, sometimes furcated, well-rounded ribs; inner volutions exposed; aperture obovate; septa 
numerous; thickness equal to one-fourth of diameter. This species is the largest of the genus. Size 
from 4 ft. downwards. 
7. A. Ellipticus. {Oval Ammonite.) Depressed, with sharp keel; inner volutions two-thirds 
exposed; ribs few, distant, broad, flat, agreeing in number with septa, and slightly curved; aperture 
oblongly elliptical. 
8. A. Cornuoides. {Little-liorn Ammonite.) Involute, depressed; with broad, flattened keel; 
whole surface, with rather prominent, distinct ribs; inner volutions considerably exposed; aperture 
sub-cordate. Diameter, If in.; thickness, f in. 
9. A. TriplicatllS. {Three-pleated Ammonite.) Discoidal, with six exposed volutions, two 
external ones, separated by a depression or flattened, spiral groove; whole external surface, with 
strong, equidistant, regular ribs ; aperture sub-cordate. Diameter, 8 in.; thickness, 2 in. 
10. A. Biplex. {Two-pleated Ammonite.) Discoidal, with six exposed volutions, separated by 
depression or flattened groove; with large, equidistant, regular, elevated ribs; dorsal margin 
rounded; aperture oblong, sub-cordate. Diameter, 8 in.; thickness, 2 in. 
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