180 CRETACEOUS LAMELLIBRANCHIA. 
1871. Prcren Manrenianus (= concenrricus), Ff. Stoliczka. Paleont. Indica, 
Cret. Fauna 8. India, 
vol. 11, p. 428. 
1879. “— cf. concentricus, C. Barrois. Ann. Soc. géol. du Nord, vol. vi, 
p. 452, pl. xu, fig. 4. 
1889. — Manrexut, 2. Holzapfel. Die Mollusk. Aachen. Kreide (Palaonto- 
eraphica, vol. xxxv), p. 235, pl. xxvi, fig. 6. 
1892. — (Cuiamys) Manrennranus, EH. Stolley. Die Kreide Schleswig- 
Holsteins (Mittheil. Min. Inst. 
Kiel, vel. i), p. 287. 
Non 1822. — concentricus, 7. Say. Journ. Acad. Nat. Sci. Philadelphia, vol. 
li, pt. 2, p. 259. 
— 1825. — — Defrance. Dict. Sci, nat., vol. xxxviui, p. 253. 
— 1887. -- — F.C. L. Koch and W. Dunker. Beitr nord-deutsch. 
Oolithgeb., p. 43, pl. v, fig. 8. 
Description.—Shell rather small, thin, ovate, dorsal third pointed ; inequilateral, 
higher than long; postero-dorsal margin straight or shghtly convex, and longer 
than the antero-dorsal, which is straight or shghtly concave. Apical angle from 
86° to 90°. Ears moderately large, rather high, unequal. 
Right valve flat, with several (usually from three to five) strong growth-ridges 
separated by considerable intervals, and fine radial and concentric ornament, which 
is often indistinct or absent on the later parts of the valve. Radial ornament con- 
sists of about eleven very slightly elevated ridges or folds, which become indistinct 
ventrally; on the summits of the ridges there are usually two fine linear ribs, and 
others (two or three) of the same kind in the shallow furrows; near the anterior 
and posterior margins the radial ridges are replaced by ribs. Concentric ornament 
consists of fine, close-set, regular, linear ridges, which bear minute pointed granules 
where they cross the radial ribs. Anterior ear considerably larger than the 
posterior, and shghtly produced dorsally, with a distinct, but not deep, sinus ; 
surface with growth-lines, which become sinuous near the valve—above the 
sinuous part there are faintly marked radial ribs. Posterior ear with an outer 
angle of about 90°, and with well-marked growth-lines. 
Left valve convex, with several strong growth-ridges at intervals. Ornamenta- 
tion consists of seventeen or eighteen main ribs, which are narrow and but little 
raised ; they are separated by broad, very shallow furrows. In the middle of each 
furrow is a similar but smaller rib, which, near the ventral border, sometimes be- 
comes almost as large as the main rib. At some distance from the umbo other 
smaller linear ribs (two to five) are introduced. In some cases all the radial ribs 
become indistinct near the ventral border, where the shell is then smooth, except for 
concentric ornament. The concentric ornament consists of regularly-placed, fine, 
linear ribs, which are more widely spaced near the umbo than elsewhere, and form 
