246 MOLLUSCA. CEPHALOPODA. Ammonita. 



in a tubercle ; apertures transverse, quadrangular, three times as wide as 

 long. — Sotver. Min. Conch, t. cci. (indistinct.) — Under Oolite. 



71. A. Sowerbii — Discoid, carinated, whorls 4, inner ones half concealed, 

 about eight spiniform tubercles upon each whorl 5 keel round, entire ; aper- 

 ture elliptical. Var. a. aperture circular ; keel sometimes impressed Sower. 



Min. Conch, t. ccxiii Under Oolite. 



72. A. Brownii. — Discoid, inner whorls half exposed, with large tubercles 

 on each side ; marginal undulations many, central ones few, rising into tu- 

 bercles ; front rounded Avith a distinct keel ; aperture cordate Sower. Min. 



Conch, t. cclxiii. f. 4, 5. — Under Oolite, Dundry. 



73. A. Birchi. — Discoid, whorls 6, exposed, increasing gradually, sides con- 

 cave, front rounded, transversely and obscurely sulcated ; two involuted rows 

 of spiniform tubercles ; aperture transverse. — Sower. Min. Conch, t. cclxvii. 

 — In Lias at Lyme. 



74. A. lauta — Discoid, inner whorls half concealed ; front narroAV, slightly 

 concave; principal ribs slender, varicose or tuberculated near their com- 

 mencement, shorter ribs alternating, united in pairs, to form compressed tu- 

 bercles upon the edges of the front. — {Park. Trans. Geol. v. 58.) Sower. Min. 

 Conch, cccix. — Mant. Suss. 91. t. xxi. f. 11. — Chalk Marl. 



75. A. tuberculata Whorls gibbose, half concealed ; front rather flat ; ribs 



arising in threes from large round tubercles, and uniting in pairs to form 

 large compressed tubercles upon each edge of the front ; aperture suborbicu- 

 lar — Sower. Min. Conch, t. cccx. f. 1, 2, 3 Chalk Marl. 



76. A. proboscidea — Whorls ventricose, partly concealed ; front concave, tu- 

 bercles upon the sides of the last whorl, and both edges of the front subcylin- 

 drical; aperture orbicular. — Sower. Min. Conch, t. cccx. f. 4, 5 — Chalk Marl. 



77- A. Gulielmii. — Lenticular, with a narrow front; whorls exposed; ribs 

 dissimilar, terminating in small tubercles, principal ribs furnished with two 

 tubercles near their commencement ; aperture elliptical — Sower. Min. Conch: 

 t. ccxi. — Middle Oolite. 



78. A. Davaisi — Whorls exposed ; sides nearly fiat, with numerous ribs, 

 and a few distant obtuse tubercles, each tubercle connected with about 4 sul- 

 ci; aperture nearly orbicular — Sower. Min, Conch, t. cccl. — In Lias, Dorset- 

 shire. 



79. A. Brodicei — Largely umbilicate, gibbose; ribs radiating, large, nu- 

 merous, terminating on the sides of the whorls by obtuse tubercles, front 

 rounded, plicated ; aperture transversely oblong, curved. — Sower. Min. Conch, 

 t. cccli Under Oolite. 



80. A. perarmata Depressed, whorls exposed ; front rounded, armed 



with two concentric rows of large pointed tubercles, connected by obtuse 

 ridges; aperture nearly orbicular — Sower. Min. Conch, t. ccclii — Under 

 Oolite. 



81. A. mutabilis Depressed ; outer whorls compressed, plain and smooth ; 



inner whorls two-thirds exposed, tuberculated, plicated; plicae interrupted 

 over the front ; aperture ovato-sagittate. — In the young state the front is 



flattened Sower. Min. Conch, ccccv. — In Clunch Clay of the Middle Oolite 



near Horn Castle. 



82. A. subarmata Depressed, concave, ribbed, inner whorls almost wholly 



exposed ; ribs curved, often united in pairs by smooth spines ; aperture trans- 

 versely oblong, arched; the spines disappear on'tlie last whorl — (Young and 

 Bird's Geol. of York. 250. t. 13. f. 3.) Sower. Min. Conch, t. ccccvii. f. 1 — 

 Lias, Whitby. 



