124- CRETACEOUS LAMELLIBRANCHIA. 



Distribution : 



(i) Lower Gttalk : Fulbourn Asylum. Zone of H. siiJygJoTjosns of Shelford, 

 Cherry Hinton, and cutting east of South Cave Station. 



(ii) Middle Ghalh : Lewes. Melbourn Rock near Hitchin. Zone of R. Cuvieri 

 of Dover. Zone of Terehratidina gracilis of Dowlands (near Rousdon), the 

 Dorset coast, Dover, the Sussex coast, Whyteleaf (Warlingham), St. Giles' Hill 

 (Winchester), Hitchin, Worsted Lodge, and Mutlow Hill (Cambs). Zone of 

 Holaster planus of Chapel Rock (Pinhay), Dover, the Sussex coast, Cheveley, and 

 Linton. Chalk Rock {Iieussianum-zowe) of Brixton, Winchester, Cuckhamsley, 

 Tliickthorn Hill, and Boxmoor. 



(iii) IT'pper Ghalh : Zone of M. cor-testudinarium of Dover, the Sussex coast, and 

 Balsham. Zone of M. cor-aiiguinum of Thanet, St. Margaret's, the Sussex coast, 

 Charlton, Gravesend, Strood, Xorthfleet, and near Hitchin. Zone of Marsvpites of 

 Thanet and the Sussex coast. Zone of A. qnadratus of Hensting Farm, Harwell 

 Road, and Hensley Lane (all near Winchester), East and West Harnham (near 

 Salisbury), and the Sussex coast. Zone of B. mncronata of the Dorset coast. 



Spondylus seeeatlts, sp. nov. Plate XXI, figs. 6 a — c, 7 a — c. 



Description. — Shell rounded, outline rather irregular, slightly inequilateral ; 

 height and length nearly equal. 



Right valve flattened or slightly concave, with numerous parallel, concentric, 

 and spiny lamince and faint radial ribs. 



Left valve moderately convex, except in small forms ; ornamented with numerous 

 small ribs, which are of equal size except on the earlier parts of the shell, where 

 ncAv ribs are being introduced ; all the ribs bear many small spines, placed regularly, 

 but on the old parts of the shell the ribs may be nearly smooth. The grooves are 

 broader than the ribs, moderately deep, and crossed by well-marked but somewhat 

 irregular, transverse, thread-like ribs. Ears with four or five ribs. 



Measurements : 



(1) (2) (3) 



Length . . .20 . .23 . .32 mm. 



Height . . . 19-5 . .23 . .29 „ 



(1) Upper Chalk {Uintacrinus-hed), Devizes Road, Salisbury. 



(2) Upper Chalk, locality unknown. 



(3) Upper Chalk (Uintacrinus-hed), Newgate, Thanet. 



Affinities. — This is similar in form to 8. latns, but is distinguished by the small 

 and regular spines, and the broader grooves between the ribs. 8. Royanus, 



