INOCERAMUS. 271 



by deep furrows. The ridges are often at unequal distances from one another; 

 some of them start from the umbo, others may be intercalated or may arise by 

 bifurcation. Fine concentric lines cover the shell and are folded where they 

 cross the ridges and furrows. 



Affinities. — Although the radial plications give a distinctive appearance to this 

 species, yet the form of the shell closely resembles that of I. concentricus, the main 

 difference being that in the former the difference in the convexity of the two valves 

 is usually less marked than in the latter. 



Types. — The type, from the Gault of Folkestone, is in the British Museum. 

 The specimens from near Lewes, Folkestone (except figs. 1 and 2), and Clophill 

 figured by Sowerby, and the specimens figured by Mantell are in the British 

 Museum. 



Distrihution. — Gault of Folkestone, Aylesford, Ringmer, Eastbourne, the Isle 

 of Wight, and Leighton Buzzard. Upper Greensand (zone of Scldcenhaclna 

 rostrata) of Blackdowu, Sidmouth, Black Ven, and Lulworth. Red Limestone of 

 Hunstanton, South Willingham (Lincolnshire), and Speeton. 



Inoceramus, sp. Text-fig. 30. 



Specimens of a large, slightly convex Inoceramus are found in the Gault 

 of Folkestone and the Upper Greensand of Potterne (Devizes) and the Isle 

 of Wight, but are not sufficiently perfect for determination. The umbones are 

 terminal, and the hinge-line is nearly at right angles to the anterior margin. The 

 anterior parts of the valves slope steeply to the margin. Small and rather 

 distant concentric ribs are present. This form shows some resemblance to /. ])ictus 

 (p. 279), but is less convex, and possesses fewer ribs. 



Inoceeamus tenuis, Mavtell, 1822. Plate XLVIII, fig. 1. Text-figs. 31, 32. 



1822. Inoceramus tenuis, G. Mantell. Foss. S. Downs, p. 132. 

 1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 170. 



? 1859. — — T. Wiltshire. Eed Chalk 'of England (Geol. Assoc), 



p. 16, pi. i, fig. 5. 

 1866. Perna lissa, H. G. Seeley. Ann. Mag. Nat. Hist., ser. 3, vol. xvii, p. 178. 



Non 1841. Inoceramus tenuis? F. A. Burner. Die Verstein. d. nord-deutsch. 



Kreidegeb., p. 62, pi. viii, 

 fig. 11. 



Description. — Shell inequivalve, very inequilateral, convex ; postero-dorsal 

 part compressed ; antero-dorsal part excavated and more or less nearly perpen- 



