PLATE XX.** 
1, 2, 3. Ammonites Elizabethse. {Elizabeth's Ammonite.) Volutions six or seven, two-thirds 
exposed; angular from series of spines on eacli dorsal edge and two rows of tubercles on sides of 
volutions; sides with transverse ribs, angular near aperture; aperture with lengthened, spatulate 
projection, its surface deeply marked by lines of growth ; back narrow, concave, ribs passing over 
it; sipliunculus not visible. 
4, 10. A. Brightii. ( Bright's Ammonite.) Discoidal, nearly smooth; with about seven two- 
thirds exposed volutions; with several flat obtuse ribs from dorsal edge, which combine into com¬ 
pressed, elongated tubercles, reaching inner margin; sipliunculus distinguished by sharp ridge on 
back. 
5, 6, 11, 12. A. Sulcatus. {Fun •owed Ammonite.) Moderately convex; with three or four x 
volutions almost wholly exposed ; crossed by alternately long and short, curved ribs; back with deep 
sulcus in young state ; when young, ribs fine, close ; back square in adult; aperture oblong. 
7. A. Comptoni. {Compton's Ammonite.) Discoidal ; with six or seven two-thirds exposed 
smooth volutions; transversely ribbed, alternately two short and one long, from dorsal margin; 
ambit rounded, with slight depression in middle, formed by ribs which nearly meet; aperture with 
spatulate projection of about l j in. long and in. wide on each side. 
8, 9. A. Lacunatus. {Fretted Ammonite.) Discoidal, with four or five half-concealed, slightly 
compressed volutions, crossed by close, curved, alternately long and short ribs, sometimes anasto- 
mising; back with single narrow sulcus, absent in young state; aperture small, oblong. 
13, 14. A. Boblayei. {Boblaye's Ammonite.) Compressed; with five rapidly increasing, two- 
thirds concealed volutions; deeply umbilicate; volutions crossed by very thick, curved ribs, pro¬ 
jecting beyond dorsal line, more flattened on outer volutions. 
15. A. Stlltchburii. {Stutchbury's Ammonite.) Discoidal; with four two-tliirds exposed 
volutions; sides with series of short, distant, curved ribs from inner sides of volutions, ending in 
compressed tubercles; beyond these, very many close-set waved ribs; back narrowed, with smaller 
ribs passing over it, and with series of sharp serrated projections on both sides; aperture with 
projecting beak. 
16. A. Fluetuosus. {Fluctuating Ammonite.) Discoidal or lenticular; surface smooth, with 
six two-thirds exposed volutions; crossed by thick, distant ribs, almost always forked for nearly 
outer half; back plain. 
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