PLATE XII. 
1. Ammonites Varicosus. ( War ted Ammonite.) Discoidal, compressed; with six or seyen exposed 
volutions; both sides, with irregular rows of tubercles upon inner margin, with large semi-lunar, curved, 
obtuse ribs ; keel distinct; aperture oblong, about one-third diameter of disk. 
2. A. Rhotomagensis. ( Rouen Ammonite.) Discoidal, thick, sub-umbilicate ; with four sub-quadrangular 
volutions, inner ones partly inserted; sides flattish, with many transverse, nearly straight, strong, prominent 
ribs, having three short blunted tubercles upon back ; aperture oblong, nearly quadrangular; septa foliaceou^. 
Greatest diameter, 12 in. 
3. A. Subradiatus. ( Subradiated Ammonite.) Lenticular, umbilicate, carinate; inner volutions con¬ 
cealed ; sides, with numerous doubly curved ribs, obscure in middle of disk, stronger on outer margin, where 
they are furcated; ambit obtuse; keel small, entire ; umbilicus small; aperture sagittate; thickness of shell 
about one-fifth of diameter. 
4. A. Taylori. ( Taylor's Ammonite.) Discoidal, with three entirely exposed volutions, inner ones small; 
the whole crossed by about twelve remote, strong, prominent ribs, all with large spiniform tubercle on each 
side of ambit; aperture transverse, nearly round ; its length not quite one- third of diameter of shell. 
5. A. Hippocastanum. ( Horse-chestnut Ammonite.) Gibbose ; umbilicated ; with four convex, deeply 
inserted, nearly concealed volutions, crossed by ten or twelve distant, almost straight, unequal, elevated 
ribs, each with three tubercles on back or ambit, and with obtuse, oblong, somewhat tubercular elevations 
on sides ; aperture transverse, obovate. 
6. A. Brevispina. (Short-spined Ammonite.) Discoidal, with five or six entirely exposed compressed 
volutions, with numerous, somewhat obtuse, slightly curved ribs, emanating from suture and passing over 
back; each rib with two small, short spines on both sides near inner and outer edges of volutions; aperture 
obovate. 
7. A. Planorbis. ( Planorbis-shaped Ammonite.) Discoidal, with three or four smooth volutions, two- 
thirds exposed, much compressed, and crossed by many very fine lines of growth; on external surface 
beautiful, irridescent reflections. 
8. A. Gulielmi. ( Williams 1 Ammonite.) Lenticular, much compressed, with narrow, fiat ambit; with 
five or six exposed volutions, crossed by numerous dissimilar, arcuated, acute ribs; each of longer ones 
with tubercle at inner end and another at about one-third of length ; here ribs divide and alternate with 
shorter, more numerous ribs, which end in a border of round, prominent, distinct tubercles on each side 
of ambit; aperture elliptical. 
9. A. Blagdeni. (Blagden’s Ammonite.) Sub-cylindrical, very deeply umbilicate, occupying entire disk; 
with five or six volutions, almost wholly exposed, crossed by many strong, radiating ribs, terminating on 
outer edge by large spiniform tubercle ; inner volutions deeply sunk; ambit very broad, slightly convex, 
fluted ; aperture transverse, quadrangular, three times as wide as long. Greatest diameter, 6$ in.; thick¬ 
ness, 4^ in. 
* • 
10. A. Leachii. (Leach's Ammonite.) Compressed; with four volutions; inuer ones half inserted; 
crossed by many undulating, prominent, frequently furcated ribs, arcuated on crossing over front, inclining 
to aperture ; ambit sharp, crenated; aperture ovate. 
• 
11. A. Corrug-atus. (Wrinkled Ammonite.) Discoidal, earinated ; with four volutions, crossed by many 
elevated, slightly curved and furcated ribs, furcations near centre; minor volutions three-fourths concealed; 
umbilicus broad, exposing part of volutions ; back obtuse, with distinct carina in centre ; aperture obovate. 
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