PLATE XVI. 
1. Ammonites Subcarinatus. ( Subcar mated Ammonite.) Discoidal, lenticular, umbilicate, sub-carinate; 
inner volutions concealed; sides slightly inflated, thick in centre; crossed by many slightly developed ribs, 
rising in umbilicus and extending to ambit, crossing it and uniting with those on opposite side ; aperture nearly 
cordate, equal to one-half diameter of disc. 
2. A. Laticostata. (Broad-ribbecl Ammonite.) Discoidal, compressed; with five exposed, flat-sided volu¬ 
tions, crossed by large, sharp, nearly parallel ribs, which, passing over ambit, unite with those of opposite side; 
all the ribs have indistinct indications of tubercles on each end ; aperture oblong. Greatest diameter, 3£ in. 
3. A. Heterophyllus. (Reversely-foliated Ammonite.) Lenticular, umbilicate; with volutions entirely 
concealed; sides convex, wholly covered with many divergent, elevated, slightly undulating stria; umbilicus 
small, deep ; ambit rounded ; aperture large, occupying nearly two-thirds of diameter of disc, elliptical, with 
slight notch for reception of preceding volution ; septa of two kinds, small, acutely angular, and large, ovate ; 
like two forms of pinnated foliage ; siphuncle near ambit. Greatest diameter, 6 J in. 
4. A. Fissicostatus. (Cleft-ribbed Ammonite.) Discoidal, with five or six two-thirds exposed, somewhat 
depressed volutions, crossed by many, strong, slightly-undulated ribs, furcated near centre, and, passing over 
rounded ambit, join with cleft ribs of opposite side; aperture sub-ovate, being five-sixths of its length in 
width. 
5. A. Gemmatus. (Gemmed Ammonite.) Discoidal, with four or five ventricose volutions, inner ones half 
exposed, much thinner on approaching centre; inner margin of volutions slightly flattened, whence emanate 
many, strong, elevated, nearly straight ribs, united at centre of sides to large, rounded, obtuse tubercles, 
whence ribs continue diagonally and terminate in large, slightly conical tubercles on both sides of broad, fiat 
ambits. Greatest diameter, 6 in. 
6. A. Sublsevis. (Half-smooth Ammonite.) Orbicular, umbilicate ; inner volutions enveloped in outer one ; 
and their crenated edges only visible within deep conical umbilicus, internally undulated, with sharp, angular 
edge; aperture semi-circular, very wide, truncated at sides ; whole outer surface smooth ; septa numerous, with 
fine, prominent undulations, divided into many rounded foliations, margins resembling pinnate leaves; 
siphunculus close to outer margin of ambit. Diameter, 5 in.; umbilicus 1£ in. wide. 
7. A. Flexicostatus. (Bent-ribbed Ammonite.) Discoidal, compressed ; with four or five two-thirds 
exposed volutions, slightly raised in centre of sides, slanting off to margins, crossed by many, elevated, bent 
ribs, becoming furcate in middle, and passing-over thin, flattened ambit, join furcations on opposite side; 
aperture oblong-ovate. 
8. A. Crassus. (Thick Ammonite.) Discoidal; with five thick, half-inserted volutions, somewhat flattened 
on sides crossed by many straight, prominent, rounded ribs, having at centre round, elevated tubercle, whence 
ribs split into two or three, divergent, smaller costse and passing over rounded ambit, unite with those of 
opposite side ; aperture sub-cordiform. 
9. A. Plicitalis. (Plaited Ammonite.) Discoidal; with six exposed volutions; sides flat, crossed by many 
equal, straight ribs, bifurcating or trifurcating towards rounded ambit, smooth in centre; aperture quad¬ 
rangular, with rounded angles, somewhat longer than wide ; septa acutely sinuated. Thickness of shell about 
one-fourtli diameter. 
10. A. Jamesoni. (Jameson's Ammonite.) Discoidal; with five or six volutions, inner ones exposed; 
crossed by large, simple, obtuse, slightly bent ribs, and passing over rounded ambit meet those on opposite side; 
aperture oblong-ovate, its length equal to twice its width. 
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