190 CRETACEOUS LAMELLIBRANCHIA. 
small ribs on the sides of the main ribs, and may perhaps be distinct, but this can 
be determined only by an examination of specimens. 
T'ypes.—The type was obtained from Lower Chalk of Childrey, near Wantage, 
and is said to be in the Oxford Museum. The type of P. jugosus is missing, and 
the locality from which it was obtained is not given by Sowerby. Mantell’s 
figured specimen, from the Chalk Marl of Hamsey, also appears to have been lost. 
Distribution.—Upper Gault (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, ete. 
Totternhoe Stone of Cherry Hinton, Burwell, Dersingham, and Hunstanton. 
H. subglobosus zone of Blue Bell Hill (Burham), Shelford, and Cherry Hinton. 
Precren (AMQUIPECTEN) PEXATUS, Sp. nov. Plate XXXVI, figs. 5 a,b, 6, 7 a,b. 
2? 1850. Proren Dusarprnt, J. de C. Sowerby, in F. Dizon. Geol. Sussex, p. 356, 
pl. xxviii, fig. 4 (? locality). 
1897. Curamys rernata, H. Woods. Quart. Journ. Geol. Soc., vol. li, p. 382 
(not the synonymy). 
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°. Kars 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 shghtly 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 longer spines; other ribs occur on the sides of the folds, and 
are introduced at different distances from the umbo, the latest rib bemg 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 with four or more radial spiny ribs, and with 
a row of spines at the dorsal edge ; byssal sinus moderately deep. 
Measurements : 
(1) (2) (3) (4) 
Length s DA : 20, : 16:0 , 11:0 mm. 
Height : 25 : 20°5 : 16°75 ; ile gn 
(1, 3) H. planus zone, Cheveley. 
(2) Upper Chalk, near Salisbury. 
(4) A. quadratus zone, Kast Harnham. 
