162 CRETACEOUS LAMELLIBRANCHIA. 
Distribution.—Upper Greensand of Great Haldon. Chloritie Marl of Kast- 
bourne. 
Prcren (CAMPTONECTES) DUBRISIENSIS, sp. nov. Plate XXIX, figs. 8 a—e. 
Deseription.—Shell ovate, height a httle greater than length, almost equilateral, 
margins evenly rounded. Umbones pointed. Apical angle about 117°. Kars 
rather large, unequal. 
Right valve flattened, nearly smooth, with a few radial ribs near the antero- 
dorsal border, and oceasional fine curving radial ornamentation like that on the left 
valve. Antero-dorsal margin slightly concave. Anterior ear long, with a deep 
byssal sinus, very sinuous growth-lines, and well-marked growth-ridges. — Posterior 
ear triangular, with radial ribs and grooves. 
Left valve moderately convex —the convexity greatest in the dorsal third, the 
ventral portions more compressed. Greater part of the surface smooth or nearly 
smooth ; a few faintly marked growth-lines. Ornamentation seen on the sides of the 
umbonal region, also at the ventral edge, and for a short distance on the inner margin 
of some of the growth-lines; it consists of faintly marked outwardly curving ribs, 
separated by very marrow grooves, which are somewhat irregular and (in well- 
preserved specimens) punctate. Anterior ear large, not sharply separated from the 
rest of the valve, ornamented by a continuation of the radial ribs and grooves of 
the umbo, some of which cut the dorsal margin obliquely; the ribs are crossed by 
faint growth-ridges. Posterior ear smaller with similar ornamentation. 
Measurements : 
(1) (2) (3) (4) 
Length : 58 : 58 ; 2 : 32 mm. 
Height . 63 . 59-5 AG : BH) ss 
(1) Totternhoe Stone, Cherry Hinton. 
(2) Chalk Marl, Burham. 
(3) Totternhoe Stone, Burwell. 
(4) H. subglobosus zone, Hitchin. 
Affinities —The ornamentation is much less developed than in P.  striato- 
punetatus ; the shell is also larger, with a wider apical angle, less elevated ears, and 
with the left anterior ear indistinctly limited. 
Remarks.—This is a comparatively rare form, which appears to be confined to 
the Chalk Marl and the zone of H. subglobosus. 
Type.—Chalk Marl of Dover, British Museum, No. 38243. 
Distribution.—Chalk Marl of Dover and Blue Bell Hill, Burham. Totternhoe 
