118 CRETACEOUS LAMELLIBRANCHIA. 



Genus — Trapezium, Megerle v. Miihlfeldt, 1811. 



(' Naturf. Freunde zvi Berlin Mag.,' vol. v, p. 68.) 



Trapezium? akcadiforme {Keeping), 1883. Plate XXIII, figs. 10, 11. 



1883. Cypeicaedia aecadifoemis, W. Keeping. Foss. etc., Neoc. Upware and 



Brickhill, p. 120, pi. vi, fig. 6. 



Description. — Shell trapezoidal, inflated; length much greater than height. 

 Dorsal and ventral margins nearly straight and nearly parallel. Posterior margin 

 oblique, straight or slightly curved, forming an obtuse angle with the dorsal 

 margin and an acute but rounded angle with the ventral margin. Anterior margin 

 rounded. Umbones near the anterior end, much curved, with a strong, rounded 

 keel extending to the postero-ventral angle. The part in front of the keel is 

 slightly concave, giving a faint sinuosity to the ventral margin of the valve. The 

 triangular part dorsal to the keel is compressed and flattened, and slopes steeply to 

 the margin. Lunule cordate. Hinge not seen. 



Ornamentation consists of small, rounded radial ribs, and, at intervals, strong 

 concentric laminar ridges ; both ribs and ridges are indistinct on the part dorsal to 

 the keel. Length 21 mm. ; height 12'5 mm. ; thickness, 13 mm. 



Affinities. — This species is more elongate, and the carina is more angular than 

 in T. squamosum (see below). 



Remarks. — The only examples seen are the type and a specimen in Mr. J. F. 

 Walker's collection. 



Type. — The type is in the Sedgwick Museum. 



Distribution. — Lower Greensand, Upware. 



Trapezium? squamosum {Keeping), 1883. Plate XXIII, figs. 12 — 15. 



1883. Cypricaedia squamosa, W. Keeping. Foss., etc., Neoc. Upware and Brick- 

 hill, p. 120, pi. vi, fig. 5. 



Description. — Shell rounded-oblong, much inflated, highest near the posterior 

 end. Dorsal margin nearly straight; the posterior forms a regular curve, which 

 passes into the slightly concave ventral margin. Dorsal part of anterior margin 

 concave, ventral part rounded. Umbones prominent, anterior, much curved. A 

 broad, rounded ridge extends from the umbo to the postero-ventral extremity and 

 divides the shell into two parts. The part in front of the ridge is slightly concave, 

 the part above is larger and convex. Lunule cordate. 



Ornamentation consists of small radial ribs, and, at rather distant intervals, 



