118 GREY CHALK MARL. 



The shape of the radii is so remarkable, that the species may be readily 

 identified. 



Tab, xxi. fig. 6, the only perfect cast hitherto discovered : from Middle- 

 ham. 



fig. 12. A fragment from Stoneham, exhibiting the flat 



sulcated ambit. 



Locahties. Middleham, Stoneham. 



33. Ammonites curvatus. Tab. xxi. fig. 18. 



Depressed, subumbiUcate, volutions deeply inserted, transversely ra- 

 diated ; radii falciform, bifurcate at the commencement, terminating in 

 broad, tubercular curved costs ; carene with a longitudinal sulcus, between 

 two marginal rows of tubercles ; aperture obtusely sagittate. 



This ammonite is nearly allied to the preceding, but is evidently a 

 distinct species. In A. falcatus the curvatures are more numerous than 

 the oblique radii ; but in the present species, the proportions are reversed, 

 t^m or three radii uniting to form one curved rib. The terminations of 

 the ribs in the latter are tubercular, and separated from each other by a 

 sulcus ; in the former they are gently curved, and appear as if folded or 

 plaited over each other. 



The umbilicus is rather deeper than in A. falcatus, and has a marginal 

 row of oblique tubercular projections, from each of which two or three 

 radii proceed to the centre of the volutions ; here they unite, and form a 

 broad curved rib, that terminates in an elongated tubercle in the margin of 

 the ambit. Another tubercle is placed on the middle of the curved part. 

 The keel is grooved, and has two rows of prominent, distinct, opposite tu- 

 bercles, formed by the termination of the ribs. 



LocaHty. Hamsey. The specimen figured was discovered by my brother, 

 and is unique. 



34. Ammonites complanatus. 



Flat, volutions wholly inserted, the inner half marked with numerous, 

 indistinct, transverse undulating striee, the outer portion plicated ; umbi- 

 licus very small, almost concealed ; carene slightly convex, its margins 



