242 MOLLUSCA. CEPHALOPODA. Ammonita. 



16. A. excavata.— -Lenticular, subumbilicate, keel sharp, crenulated; whorls 

 C, 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. Walcottii. — Depressed, 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. angulata. — Whorls 6, exposed, with an inner marginal groove ; 'ribs 

 prominent, divided over the rounded front — Sower. Min. Conch, t. 107. f. 1. 

 — In Lias, Whitby. 



19. A. communis. — Whorls 6, exposed, rounded, ribs prominent, divided and 

 anastomosing on the outer margin ; aperture circular. — Sower. Min. Conch. 

 t. 107- f. 2, 3 In Lids, Whitby. 



20. A. Nutfaldiensis — 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, whorls 5, exposed ribs rounded, alternately 



entire and short, sometimes bifurcated ; aperture ovate. Sometimes 2 feet 

 and upwards in diameter. — List. Conch, t. 1046. Sower. Min. Conch, t. cxxvi. 

 — Upper Oolite, Wilts. 



22. A. Bucklandi Depressed, whorls 5, exposed, back flattish, with two- 

 concentric grooves, and an intermediate keel ; ribs large, obtuse, swollen to- 

 wards the back ; aperture quadrate — Sower. Min. Couch, t. cxxx — In Lias, 

 Bath. 



23. A. Conybeari 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.-c-In Lias, 

 Bath. 



25. A.fimbriata — 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. obtnsa. — 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. Brackenridgii — 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 Sower. Min. Conch, t. cxc. — In Lias at Lyme. 



30. A. Stokesi — Lenticular, depressed ; inner whorls half exposed, keel 

 crenated, ribs broad, undulated, and slightly elevated ; aperture sagittate. — 

 Soieer. Min. Conch, t. cxci. — Under Oolite, Dorset. 



