SPONDYLUS. 133 
brightoniensis by Mantell, occur chiefly in this zone, but occasionally in the 
previous zone (Pl. XXIV, fig. 3). 
Marsupites-zone. 
Two types occur : (1) with few or no intermediate ribs and the 
valves of nearly equal convexity (Pl. XXIV, figs. 4, 6); (ii) with many inter- 
mediate ribs of nearly the same size as the main ribs, and valves of nearly equal 
convexity : this is not so common as the first type (Pl. XXIV, fig. 5). 
A. quadratus-zone.—The same two types occur. Only a few examples have 
been seen, the average size being apparently less (Pl. XXIV, fig. 7). 
B. mucronata-zone.—No intermediate ribs in the examples seen (similar to 
Pl. XXIV, fig. 4). 
Trimingham Chalk.—Two rather small examples are in Mr. A. C. Savin’s 
collection, one without intermediate ribs, and the other haying four. Another 
specimen is in Mr. R. M. Brydone’s collection. 
Types.—Sowerby’s types from Brighton and Northfleet are in the British 
Museum. I have not seen the specimen figured by Mantell as Plagiostoma spinosa, 
nor the type of P. brightoniensis. S. superbus, Willett, MS., is in the Brighton 
Museum. The types of S. duplicatus, Goldfuss, came from the Senonian of 
Quedlinbure and Coesfeld. 
Distribution.—S. spinosus ranges from the zone of Rhynchonella Cuvieri to zone 
of B. mucronata. A few of the localities are given below. 
i. Zone of R. Cuviert.—Dover. 
iu. Zone of Terebratulina gracilis—Dowlands (near Rousdon). Whitecliff 
(Seaton). Hooken (near Beer Head). St. Giles’s Hill and Twyford Down (Win- 
chester). East Knoyle (Wilts). The Sussex coast. Dover. Whyteleaf (War- 
lingham). Dunton Green. Preston (Hitchin). Luton. 
iii. Zone of Holaster planus.—Chapel Rock (Pinhay). St. Giles’s Hill (Win- 
chester). The Sussex coast. Dover. Cuxton. Borstal. Cheveley (Newmarket). 
Three quarters of a mile north-west of West Wratting (Cambs). 
iv. Chalk Rock.—West Wycombe. Princes Risborough. Cuckhamsley. Box- 
moor. Luton. Clothall (Herts). Quickwood (Herts). Reed and Newsells 
(Royston). Underwood Hall (Dullingham). Barkway. Great Chesterford. 
v. Zone of Micraster cor-testudinarium.—West of Beer Harbour. North of 
Alton Line Junction. The Sussex coast. Dover. Chatham. Purley. Balsham. 
vi. Zone of Micraster cor-anguinum.—Hungry Down, Blandford. Mitcheldever 
(upper part of zone). Eaton Lane and Winnal Road (Winchester). The Sussex 
coast. St. Margaret’s. Thanet. Gravesend. 
vii. Zone of Marsupites testudinarius—Witherington, near Salisbury (lower 
part of zone). Devizes Road, near Salisbury (Uintacrinus-band). The Sussex and 
Thanet coasts. Margate. 
vii. Zone of Actinocamax quadratus—The Dorset coast. East and West 
