242 MOLLUSCA. CEPHALOPODA. Ammonita. 
16. K.excamta. — Lenticular, subumbilicate, keel sharp, crenulated; whorls 
G, in full-grown shells three -fourths concealed; ribs curved, obscure; aper- 
ture sagittate, the inner angles truncated. — Sower. Min. Conch, t. 105. — In 
Middle Oolite^ Shotover, Oxford. 
17- A. lFa/coif^M.---I)epressed, whorls 4, three-fourths exposed, with, a con- 
centric smooth furrow along the inner margin ; the keel with lateral furrows ; 
sides flattish, with obscure lunate ribs ; aperture oblong. — Sower. Min. Conch, 
t. 106. — In Lias. 
18. A. angidata . — Whorls 6, exposed, with an inner marginal groove; fribs 
prominent, divided over the rounded front. — Sower. Min. Conch, t. 107. f* 1. 
— In LiaSy Whitby. 
19. A., communis . — Whorls 6, exposed, rounded, ribs prominent, divided and 
anastomosing on the outer margin ; aperture circular.— *S'ozm’. Min. Conch, 
t. 107. f. 2, 3 — In Lias., Whitby. 
20. A. Nutfieldiensis — Whorls 4, half concealed, front rounded ; ribs nu- 
merous, prominent, rounded, with short intermediate ones on the front ; par- 
titions numerous ; aperture cordate — Sower. Min. Conch, t. cviii — In Green 
Sand. • 
21. A. gigantea — Depressed, Avhorls 5, exposed ribs rounded, alternately 
entire and short, sometimes bifurcated ; aperture ovate. Sometimes 2 feet 
and upwards in diameter. — List. Conch. 1. 1046. Sower. Min. Conch, t. cxxvi, 
— Upper Oolite., Wilts. 
22. A. Bucklandi. — Depressed, Avhorls 5, exposed, back flattish, with two 
concentric grooves, and an intermediate keel ; ribs large,^obtuse, swollen to- 
wards the back ; aperture quadrate — Sower. Min. Conch, t. cxxx. — In Lias, 
Bath. 
23. A. Cmybeari. — Depressed, whorls 8, exposed, keel large, with a shal- 
low groove on each side ; ribs large, rounded ; aperture oblong — Sower. Min. 
Conch, t. cxxxi — In Lias, Bath. 
24. A. Greenoughi — Depressed, whorls 4, two-thirds concealed, obscurely 
undulated, back rounded ; chambers numerous ; aperture elliptical, deeply 
indented by the preceding whorl. — Sower. Min. Conch, t. cxxxii In Lias, 
Bath. 
25. A. Jimbriata — Whorls cylindrical, exposed ; lines of growth obtuse or 
acute, undulated or fimbriated ; shell thin, margins of the septa with rounded 
lobes ; mouth orbicular. — Sower. Min. Conch. t.|clxiv — In Lias at Lyme Regis. 
26. A. plicatilis — Whorls 6, exposed, sides flat, front round, plain in the 
centre ; ribs numerous, equal, straight, furcate ; septa acutely sinuated ; 
aperture squarish, with rounded angles. — Sower. Min. Conch, t. clxvi In 
Middle Oolite, Berkshire. 
27- A. obtusa — Whorls 4, exposed ; front with two slight furrows and an 
obtuse keel ; ribs large, curved, sharpest in the middle ; aperture oblong.—- 
Sower. Min. Conch, t. clxvii — In Lias, Lyme Regis. 
28. A. Bracltenridgii — Depressed, front rounded, whorls 3, exposed ; ribs 
prominent, numerous, sharp and furcate ; lip expanded into two oblong lobes. 
— Sower. Min. Conch, t. clxxxiv . — Under Oolite, near Bristol. 
29. A. Brooki . — Whorls 4 or 5, the inner ones half exposed, depressed, ca- 
rinated, with a sulcus on each side the keel, ribs strong, simple, arched ; aper- 
ture oblong.— Min. Conch, t. cxc. — In Lias at Lyme. 
30. A. Stdkesi — -Lenticular, depressed ; inner whorls half exposed, keel 
crenated, ribs broad, undulated, and slightly elevated ; aperture sagittate. — 
Soxcer. Min. Conch, t. cxci . — Under Oolite, Dorset. 
