162 CRETACEOUS LAMELLIBRANCHIA. 



Distribution. — Upper Greensand of Great Haldon. Cliloritic Marl of East- 

 bourne. 



Pectkn (Camptonectes) dubeisiensis, sp. nov. Plate XXIX, figs. 8 a — c. 



Description. — Shell ovate, lieight a little greater than length, almost equilateral, 

 margins evenly rounded. Umbones pointed. Apical angle about 117°. Ears 

 rather large, unequal. 



Right valve flattened, nearly smooth, with a few radial ribs near the antero- 

 dorsal border, and occasional fine curving radial ornamentation like that on the left 

 valve. Antero-dorsal margiu 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 narrow grooves, which are somewhat irregular and (in well- 

 preserved specimens) punctate. Anterior ear large, not sharply separated from the 

 rest of the valve, ornamented l)y 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 . 42 . 32 mm. 



Height . 63 . 59-5 . 46 . 35 „ 



(1) Totternlioe Stoue, Cherry Hinton. 



(2) Chalk Marl, Burham. 



(3) Totternhoe Stone, Burwell. 



(4) H. suhfjlohosus zone, Hitcliin. 



Affinities. — The ornamentation is much less developed than in P. striato- 

 punctatas ; the shell is also larger, with a wider apical angle, less elevated cars, and 

 with the left anterior ear indistinctly limited. 



llemarks. — This is a comparatively rare form, which appears to be confined to 

 the Chalk Marl and the zone of H. subglobosus. 



Type.— C\m\k Marl of Dover, British Museum, No. 38243. 



Distribution. — Chalk Marl of Dover and Blue Bell Hill, Burham. Totternhoe 



