PLATE VI. 
1. Ammonites Brongniarti. ( Brongniarte’s Ammonite.) Gibbous; thickness about two- 
thirds diameter; minute umbilicus ; inner volutions concealed; whole surface with close, undulating, 
regular, rather depressed, furcated radii; aperture placed transversely, with a thick, inflected lip. 
2. A. Calloviensi. (Kelloway’s Ammonite.) Involute, sub-umbilicate, with five volutions, 
three-fourths concealed; ambit depressed; with very many small, bent, radiating ribs, arranged in 
sets; aperture deltoidal, with truncated angles; siphuncle placed near upper edge. Greatest dia¬ 
meter, 3 in. 
3. A. Gervilii. ( De Gerville's Ammonite.) Gibbous, largely umbilicate, exposing ribbed mar¬ 
gins of volutions; thickness rather more than half diameter; with sharp, numerous, close, regular, 
bent, furcated ribs; inner volutions slightly exposed; aperture transversely oblong, excavated; lip 
sharp on edge, arched. 
4. Vide Plate IY. 8. 
5. A. Nutfieldensis. ( Nutfield Ammonite.) Involute, with four or five volutions, much con¬ 
cealed ; crossed by numerous, strong, prominent ribs, with intermediate shorter ones; septa rather 
numerous; aperture sitb-cordiform; two-fifths of diameter in length, nearly same in width. Dia¬ 
meter, 3 in. to 1 ft. 
6. A. Triplicatus. ( Three-pleated Ammonite.) Involute, with four volutions, inner ones ex¬ 
posed ; surface, with doubly curved, long and short ribs; septa distant; aperture obovate, about 
half diameter in length and one-third in width. 
7. A. Excavatus. (Hollow Ammonite.) Involute, lenticular, sub-umbilicate; with sharp, 
crenulated carina; volutions about six, wholly exposed in young state; entire shell with obscure, 
curved ribs; aperture sagittate; about half diameter of shell. Greatest diameter, 4 in. 
8. A. JilgOSUS. (Ridged Ammonite.) Involute, with small, distinct carina; four volutions 
half-concealed ; with large, obtuse, straight ribs, very regular; septa not numerous; margins of same 
plaited; aperture ovate, narrower behind, about two-fifths diameter of shell and width one-fifth; 
shell delicate, very thin. 
9. A. Communis. (Common Ammonite.) Involute, with six or eight rounded, wholly ex¬ 
posed volutions; crossed by numerous, strong, prominent, straight ribs, furcated towards dorsal 
margin, and sometimes re-united on ambit and again divided on opposite side of shell; aperture three- 
fourths of a circle and about one-fifth diameter of shell; septum round. 
10. A. Angulatus. (Angulated Ammonite.) Involute, with seven or eight rounded, wholly 
exposed volutions, angular along their inner sides, and divided by a narrow, concave, flattened space, 
whence numerous, prominent ribs; aperture somewhat longer than wide, width being equal to about 
one-fifth diameter of shell; sinuated margins of septa rather close. 
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