242 MOLLUSCA. CEPHALOPODA. Ammonita. 



16. A. cj?cauato.— Lenticular, subumbilicate, keel sharp, crenulated; whorls 

 6, in fuU-grown shells three-fourths concealed ; ribs curved, obscure ; aper- 

 ture sagittate, the inner angles truncated. — Sower. Mm. 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 — Soiver. Aim. Conch. 

 t. lOG 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. £ 1. 

 — In Lias, Whitbv. 



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

 anastomosing on the outer margin ; aperture cii-cular. — Soicer. ]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. ffigantca Depressed, whorls 5, exposed ribs rounded, alternately 



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

 and upwards in diameter. — List. Conch. 1. 1046. Soiver. Min. Conch, t. cxxvi. 

 — Upper Oolite, AVilts. 



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. Alin. Conch, 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, deeph' 



indented by the preceding whorl — Sower. Min. Conch, t. cxxxii In Lias, 



Bath. 



25. A. fimhriata — Whorls cylindrical, exposed ; lines of growth obtuse or 

 acute, undulated or fimbriated ; shell thin, margins of the septa with rounded 

 lobes; mouth orbicular — Soiver.'Mm. Conch. t.|clxiv — In //io* at Lyme Regis. 



26. A. plicatilis — Whorls 6, exposed, sides flat, front round, plain m 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. obtitsa. — Wliorls 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 ; Up expanded into two oblong lobes. 

 — Sower. Min. Conch, t. clkxxiv Under Oolite, near BristoL 



29. A. Brooki Whorls 4 or 5, tlie 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.— 

 Sower. ]\Iin. Conch, t. cxqi,— Under Oolite, Dorset. 



