100 CRETACEOUS LAMELLIBRANCHIA. 



small ril:)S on the sides of tlie main ribs, and may perhaps l)e distinct, but this can 

 be determined only by an examination of specimens. 



Types. — The type was obtained from Lower Chalk of Childrey, near Wantage, 

 and is said to be in the Oxford Mnsenm. The type of P. jiigosus is missing, and 

 the locality from which it was obtained is not given by SoAverby. Mantell's 

 fignred specimen, from the Chalk Marl of Hamsey, also appears to have been lost. 



Distribution. — Upper Ganlt (zone x) of Folkestone. Red Limestone of 

 Hunstanton {fide Survey Memoirs). Chloritic Marl of Blackgang and Niton. 

 Chalk Marl of Ventnor, Folkestone, Meldreth, Hunstanton, Stoke Ferry, etc. 

 Totternhoe Stone of Cherry Hinton, Burwell, Dersingham, and Hunstanton. 

 H. subglobosus zone of Blue Bell Hill (Burham), Shelford, and Cherry Hinton. 



Pecten (^^uipecten) pexatus, sp. nov. Plate XXXVI, figs. b(i,h, G, 7 ((,b. 



? 1850. Pecten Dujardini, /. de C. Suwerbi/, iu F. Dixon. Geol. Sussex, p. 356, 



pi. xxviii, fig. 4 (? locality). 

 1897. Chlamys ternata, H. Woods. Quart. Jouru. Gool. Soc, vol. liii, p. 382 



(not the syuonyuiy). 



Description. — Shell small, ovate or nearly circular, pointed dorsally, equi- 

 lateral, and almost equivalve ; of slight convexity. Length usually a little less 

 than height. Apical angle about 104°. Ears fairly large. 



Both valves have radial folds, of slight elevation, and usually eleven in number. 

 The entire surface is ornamented with numerous narrow, elevated, and sharply 

 limited ribs, which are placed regularly, are of slightly unequal size, and bear many 

 short, hollow spines, which are generally directed ventrally, but are sometimes 

 nearly perpendicular. At the summit of each fold is a rib rather larger than the 

 others, and bearing longci' s|niies; other ribs occur on the sides of the folds, and 

 are introduced at different distances from the umbo, the latest rib being the 

 smallest. On each side of a fold, near the margin of the valve, there are generally 

 three, but sometimes more ribs. 



Ears slightly unequal, ornamented Avith four or more radial spiny ribs, and Avitli 

 a row of spines at the dorsal edge ; byssal sinus moderately deep. 



J 



easurements : 













(1) 



(2) 



(3) 



(4) 



Length 



24. 



20 



l()-0 



11-0 mm. 



Height 



25 



20-5 



10-75 



11-5 „ 



(1, o) If. planus zoijc, Clicveley. 

 (2) Upper Chalk, uear Salisbury. 

 (4) A. quadratus zone, East Haruham. 



