180 CRETACEOUS LAMELLIBRANCHIA. 



1871. Pecten Mantellianus (= concentricus), F. Stoliczka. Palseont. Iiidica, 



Cret. Fauna S. India, 

 vol. iii, p. 428. 

 1879. -— cf. CONCENTRICUS, C. Bavrois. Ann. Soc. gcol. dvi Nord, vol. vi, 



p. 452, pi. xii, fig. 4. 

 1889. — Ma-ni-eIj-li, E. Hohapfel. Die Mollusk. Aachen. Kreide (Palseonto- 



graphica, vol. xxxv), p. 235, pi. xxvi, fig. 6. 

 1892. — (Chlamys) Mantellianus, E. Stolley. Die Kreide Sdileswig- 



Holsteins (Mittheil. Min. Inst. 

 Kiel, vol. i), p. 237. 



Non 1822. — concentricus, T. Say. Journ. Acad. Nat. Sci. Philadelphia, vol. 



ii, pt. 2, p. 259. 



— 1825. — — Befrance. Diet. Sci. uat., vol. xxxviii, p. 253. 



— 1837. — — F. C.L. Koch and W. Bunker. Beitr nord-deutsch. 



Oolithgeb., p. 43, pi. v, fig. 8. 



Description. — Shell rather small, thin, ovate, dorsal third pointed ; inequilateral, 

 higher than long ; postero-dorsal margin straight or slightly convex, and longer 

 than the antero-dorsal, which is straight or slightly 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 slightly 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, wery 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 riljs, which arc moi'o widely spaced near the umbo than elsewhere, and form 



