336 CRETACEOUS LAMELLIBRANCHIA. 



Inoceeamus costellatus, sp. nov. Plate LIV, figs. 5 — 7. 



1897. Inoceeamus, sp., H. Woods. Quart. Journ. Geol. Soc, vol. liii, p. 381, 



pi. xxvii, figs. 14 — 17. 



Description. — Shell small, vei\y inequilateral, rather hig-lier than long, of 

 moderate convexity — the greatest convexity being between the umbones and the 

 postero-ventral extremity. Umbones terminal. Hinge equal to about three- 

 quarters of the length of the shell, and forming more than a right angle with the 

 anterior margin. Anterior margin moderately convex, ventral margin very 

 convex, posterior margin slightly convex. 



Right valve with a small, pointed, slightly curved umbo. Posterior and postero- 

 dorsal parts of the valve flattened A small, flattened antcro-dorsal area is nearly 

 perpendicular to the plane of the valves. 



Left valve more convex than the right ; postero-dorsal part compressed, but 

 not forming a definite ear. Umbo narrow, pointed, curved inwards, larger and 

 more prominent than tlie umbo of the right valve. Antero-dorsal area larger 

 than on the right valve. 



Concentric ribs narrow, sharp, usually widely separated; interspaces broad 

 and shallow. The curvature of the ribs is very unsymmctrical ; the ventral part 

 is very convex, the posterior part only slightly convex. 



Bemarlis. — This species is fairly common in the Chalk Rock. All the speci- 

 mens seen are casts. Some examples, Avhich appear to be a variety of this species, 

 have small ribs of uniform size. 



Affinities. — This species appears to be related to some foi-ms of /. Lainarrl-i, 

 Parkinson, but the left umbo is narrower, more pointed, and less curved ; the line 

 of gTeatest convexity is more oblique to the hinge-line, and the posterior and 

 postero-dorsal parts of the valves are more conijiressed.' 



Type. — From the Chalk Rock of Cuckhamsley, in the Sedgwick Museum, 

 Cambridge. 



Distribution. — Chalk Rock of Dover, Guilford Colliery (Coldred near Dover), 

 the Sussex Coast, south-east of Calstone Willington, Cuckhamsle}', Blount's Farm 

 near Marlow, Luton, Wallington near Baldock, ]3arley near Royston, and 

 Underwood Hall near Dullingham. Zone of HoJastcr jilnnns of South Devon, the 

 Dorset Coast, the Isle of Wight, Lichfield (Hants), Winchester, etc." 



' Corapaiv also /. iinJulaliis, Eogala, • Bull. luteruat. Acad. Sci. Cracovie' (1911), p. 171, pi. iv, 

 fig. 7, and /. Frecld, Audert, ' Inooeraineu d. Kreibitz-Zittauer Sand stein geb.' (1911), p. 51, pi. i, 

 fig. 8. 



2 Recoi'ded iiy Rowe froui tlic zones of Terebraluliiia lata and Micraster cor-anguinum of Dover. 



