PLATE XVIII. 
1. Ammonites Marginatus. ( Bordered Ammonite.) Sub-globose, umbilicate, carinated; edges of inner 
volutions only visible in large, deep, conical umbilicus with sub-carinated margin, and series of round, promi¬ 
nent tubercles about its edge; outer volution very large, thick, wrinkled transversely; carina prominent, 
sharp. 
2. A. Maculatus. ( Spotted Ammonite.) Discoidal, thick ; with five or six exposed volutions, with flattened 
sides, crossed by many straight, elevated ribs, from inner margins, passing over broad, flat ambit to inner 
margins of volutions on opposite side ; aperture nearly orbicular. 
B. A. Sigmifer. ( S-ribbcd Ammonite.) Discoidal, carinated; with four compressed volutions, crossed by 
distant, curved ribs ; inner volutions half-concealed, increasing rapidty ; carina sharp, broad. 
4. A. Discus. (Quoit Ammonite.) V. Plate IX., fig. 4. 
5. A. Compressus. ( Compressed Ammonite.) Elliptical, smooth, compressed ; with four or five flat volu¬ 
tions, almost wholly exposed ; inner margin of volutions flat, perpendicular to sides ; ambit broad, flat; aperture 
oblong, rectangular. Greatest diameter, 71 in. 
6. A. Multicostatus. (. Many-ribbed Ammonite.) Discoidal, much depressed, carinate; with three or four 
wholly exposed volutions; crossed by many strong, sharp, slightly-bent ribs, with depressed, blunt, oblong 
tubercle on outer extremity of each, extending over ambit almost to dorsal sulcus; carina slightly elevated, 
with sulcus on both sides; aperture oblong, its length more than one-fourth diameter of last volution. 
Greatest diameter, 14 in.; thickness, 3 in. to 4 in. 
7. A. Monile. (. Necldace Ammonite.) Discoidal, thick, sub-umbilicate ; with four wholty-exposed volutions, 
crossed by many crnwed, tubercular ribs ; tubercles hollow; whole surface crossed by very fine, divergent striae ; 
ambit somewhat concave with close, transverse striae ; aperture transversely ovate, about one-third diameter of 
shell long and almost twice as wide. 
8. A. Crenularis. {Crenulated Ammonite.) Lenticular, umbilicate; with five, two-thirds inserted volutions; 
umbilicus deep ; outer volution thick in centre ; ambit sharp, thin ; sides, with series of strong, elevated, remote 
ribs, met at centre by many smaller, oblique ones passing over crenulated ambit; aperture nearly cordiform, its 
length almost equal to half diameter of disc ; width about half its length. 
9. A. Inflatus. ( Inflated Ammonite.) Depressed, carinated; inner volutions wholly exposed, outer one 
inflated towards aperture; sides flattened, crossed by large, elevated, strong ribs, each commencing with large, 
compressed tubercle on inner end, furcated towards ambit; all the branches of ribs end in elongated, compressed 
tubercles on margin of flattened ambit; carina distinct, entire, obtuse; aperture somewhat quadrangular. 
10. A. Braikenridgii. {Braikenridge’s Ammonite.) Discoidal, compressed; with three or four volutions, 
inner ones exposed, outer ones rather less than one-third diameter of disc broad; crossed by many narrow, acute 
ribs from internal margin of volutions, and almost immediately furcate ; at base of each furcation ribs with 
small, blunted tubercle ; aperture orbicular; tip expanded into two oblong lobes. 
11. A. Clevlandicus. ( Clevland Ammonite.) Discoidal; with five volutions, inner ones nearly half- 
inserted ; with series of straight, sharp ribs from inner margin, terminating about centre of volutions in oblong, 
blunted tubercle ; toward aperture ribs longer, thickened externally; all met by many smaller, nearly obsolete 
ribs passing over thin ambit, producing crenulated, sub-carinated centre ; aperture nearly cordiform. 
12. A. Heterogenus. {Heterogenus Ammonite.) Discoidal, somewhat compressed; volutions few, outer one, 
crossed by fourteen thick, depressed, rounded ribs, passing over scalloped ambit; ribs met by narrow, straight 
ribs, rising on inner margin and terminating at about three-fourths across shell. 
13. A. Erugatus. {Wrinkled Ammonite.) Discoidal, thick; with five volutions almost wholly exposed; 
crossed by obsolete ribs; ambit rounded ; aperture oblong-ovate, indented by preceding volution; its length 
about one-third diameter of disc. 
14. A. Funatus. {Ropy Ammonite.) Elliptical; with three or four half-concealed volutions, crossed by 
many simple, rounded, rope-like ribs, separated by wide grooves, constricted at intervals; aperture semi-lunar. 
Greatest diameter, 3 in.; thickness, 1\ in. 
15. A. Anguiliferus. {Hook-ribbed Ammonite.) Discoidal, with five almost wholly exposed volutions, 
crossed by many elevated ribs, passing over thin ambit in a hooked form ; aperture somewhat cordiform. 
( 19 ) 
